Past Contests
Ongoing and upcoming contests

OMO Spring 2020
OMO Spring 2020, March 27–April 7, 2020 (Fri–Tue)
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Mar 27 4:00 PM PDT to Tue, Apr 7 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring20Problems.pdf
 Problem answers
 Show

OMO Fall 2019
OMO Fall 2019, October 25  November 5, 2019 (Fri  Tue)
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Oct 25 4:00 PM PDT to Tue, Nov 5 4:00 PM PST
 Teams
 View Team
 Duration
 265 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall19Probs.pdf
 Problem answers
 Show

OMO Spring 2019
OMO Spring 2019, March 22  April 2, 2019 (Fri  Tue)
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Mar 22 4:00 PM PDT to Tue, Apr 2 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring19Probs.pdf
 Problem answers
 Show

OMO Fall 2018
OMO Fall 2018, October 26  November 6, 2018 (Fri  Tue)
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Oct 26 4:00 PM PDT to Tue, Nov 6 4:00 PM PST
 Teams
 View Team
 Duration
 265 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall18Probs.pdf
 Problem answers
 Show

OMO Spring 2018
OMO Spring 2018. March 23  April 3, 2018 Fri  Tue
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Mar 23 4:00 PM PDT to Tue, Apr 3 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring18Probs.pdf
 Problem answers
 Show

OMO Fall 2017
OMO Fall 2017. October 27  November 7, 2017 Fri  Tue
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Oct 27 4:00 PM PDT to Tue, Nov 7 4:00 PM PST
 Teams
 View Team
 Duration
 265 hours and 0 seconds
 Number of problems
 30
 Problems file
 Fall_2017_OMO.pdf
 Problem answers
 Show

Summer Contest 2017
NIMO summer contest
 Type
 Summer Contest (Rules)
 Contest window
 Sat, Aug 19 4:58 PM PDT to Sat, Aug 19 5:18 PM PDT
 Duration
 15 minutes and 0 seconds
 Number of problems
 15
 Problem weights
 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 (Total: 120.0)
 Problems and answers
 Problems and answers
 Penalty per minute spent on correct problems
 1.0

Contest 32
May 2017 monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Thu, May 11 4:55 PM PDT to Thu, May 11 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 5
 Problem weights
 8.0, 10.0, 11.0, 13.0, 14.0 (Total: 56.0)
 Problems file
 NIMO032.pdf
 Problem answers
 Show
 More details
 Show

Revenge 31
Our annual contest in which the contestants write the problems!
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Apr 7 4:55 PM PDT to Fri, Apr 7 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO031.pdf
 Problem answers
 Show
 More details
 Show

April 2017 Fun Round
April Fool's round for 2017.
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Mar 31 9:00 PM PDT to Sat, Apr 1 8:59 PM PDT
 Duration
 24 hours and 0 seconds
 Number of problems
 8
 Problem weights
 50000.0, 50000.0, 60000.0, 60000.0, 70000.0, 80000.0, 90000.0, 100000.0 (Total: 560000.0)
 Problems file
 Endeavor.pdf
 Problem answers
 Show
 More details
 Show

OMO Spring 2017
Spring OMO 2017 March 24  April 4, 2017 Fri  Tue
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Mar 24 4:08 PM PDT to Tue, Apr 4 5:00 PM PDT
 Teams
 View Team
 Duration
 264 hours, 52 minutes and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring17Probs.pdf
 Problem answers
 Show

Contest 30
February 2017 monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Thu, Feb 16 4:55 PM PST to Thu, Feb 16 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO030.pdf
 Problem answers
 Show
 More details
 Show

Contest 29
November 2016 monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Wed, Nov 30 4:55 PM PST to Wed, Nov 30 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO029.pdf
 Problem answers
 Show
 More details
 Show

Fall Online Math Open
Fall OMO 2016. You get an extra hour due to daylight savings time :)
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Nov 4 4:00 PM PDT to Tue, Nov 15 4:00 PM PST
 Teams
 View Team
 Duration
 265 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall16Probs.pdf
 Problem answers
 Show

Contest 28
October 2016 monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Tue, Oct 18 4:55 PM PDT to Tue, Oct 18 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO028.pdf
 Problem answers
 Show
 More details
 Show

Contest 27
September 2016 monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Sep 26 4:55 PM PDT to Mon, Sep 26 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO027.pdf
 Problem answers
 Show
 More details
 Show

NIMO Summer Contest 2016
Summer Contest rules; 15 problems in 15 minutes.
 Type
 Summer Contest (Rules)
 Contest window
 Sat, Aug 6 4:58 PM PDT to Sat, Aug 6 5:17 PM PDT
 Duration
 15 minutes and 0 seconds
 Number of problems
 15
 Problem weights
 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 (Total: 120.0)
 Problems and answers
 Problems and answers
 Penalty per minute spent on correct problems
 1.0

Contest 26
May contest; 5 problems in 40 minutes.
 Type
 Monthly Contest (Rules)
 Contest window
 Thu, May 12 4:55 PM PDT to Thu, May 12 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 5
 Problem weights
 5.0, 7.0, 8.0, 10.0, 12.0 (Total: 42.0)
 Problems file
 NIMO026.pdf
 Problem answers
 Show
 More details
 Show

Revenge 25
NIMO Contest 25, with student submissions
 Type
 Monthly Contest (Rules)
 Contest window
 Tue, Apr 5 4:55 PM PDT to Tue, Apr 5 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO025.pdf
 Problem answers
 Show
 More details
 Show

April 2016 Fun Round
An April Fool's round for 2016.
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Apr 1 12:00 AM PDT to Fri, Apr 1 11:59 PM PDT
 Duration
 24 hours and 0 seconds
 Number of problems
 8
 Problem weights
 31.0, 41.0, 26.0, 59.0, 53.0, 58.0, 97.0, 93.0 (Total: 458.0)
 Problems file
 Rhapsody.pdf
 Problem answers
 Show
 More details
 Show

Spring 2016 Online Math Open
OMO Spring 2016, 30 problems as usual.
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Mar 18 4:00 PM PDT to Tue, Mar 29 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring16Probs.pdf
 Problem answers
 Show

Contest #24
February contest
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Feb 22 4:55 PM PST to Mon, Feb 22 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO024.pdf
 Problem answers
 Show
 More details
 Show

Contest #23
January contest
 Type
 Monthly Contest (Rules)
 Contest window
 Thu, Jan 7 4:55 PM PST to Thu, Jan 7 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO023.pdf
 Problem answers
 Show
 More details
 Show

Revenge 22
NIMO Contest 22, with student submissions
 Type
 Monthly Contest (Rules)
 Contest window
 Tue, Dec 8 4:55 PM PST to Tue, Dec 8 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO022.pdf
 Problem answers
 Show
 More details
 Show

Fall OMO 2015
Online Math Open team contest for November 2015. Teams consist of up to four students. NOTE: the start and end time were originally set in the incorrect time zone. Please take note that the start/end time for this contest is 7 PM *Eastern Time*.
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Nov 6 4:00 PM PST to Tue, Nov 17 4:00 PM PST
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall15Probs.pdf
 Problem answers
 Show

Contest #21
NIMO Contest for October 2015.
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Oct 16 4:55 PM PDT to Fri, Oct 16 5:40 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO021.pdf
 Problem answers
 Show
 More details
 Show

Contest #20
NIMO contest for September 2015.
 Type
 Monthly Contest (Rules)
 Contest window
 Wed, Sep 23 4:55 PM PDT to Wed, Sep 23 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO020.pdf
 Problem answers
 Show
 More details
 Show

Summer Contest 2015
You may start up to two minutes early and up to two minutes late, but regardless of the start time your contest ends when 15 minutes expires or 5:17 occurs, whichever is sooner.
 Type
 Summer Contest (Rules)
 Contest window
 Sat, Aug 8 4:58 PM PDT to Sat, Aug 8 5:17 PM PDT
 Duration
 15 minutes and 0 seconds
 Number of problems
 15
 Problem weights
 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 (Total: 120.0)
 Problems and answers
 Problems and answers
 Penalty per minute spent on correct problems
 1.0

Contest 19
May Contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Tue, May 19 4:55 PM PDT to Tue, May 19 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 5
 Problem weights
 5.0, 7.0, 8.0, 10.0, 12.0 (Total: 42.0)
 Problems file
 NIMO019.pdf
 Problem answers
 Show
 More details
 Show

Spring OMO 2015
The Spring installment of the 20142015 OMO contests. NOTE: In #29 the side length of BC should be 20x^(5/2), not 10x^(5/2). The original formulation of the problem leads to a unique value of x, but for which the resulting triangle ABC does not fit the problem criteria. The new formulation fixes this issue. We will grade as correct the answer obtained under either formulation, i.e., if your team solved the original version of the #29 there is no need to redo the problem as the answer originally submitted will still be graded correct.
 Type
 Omo Contest (Rules)
 Contest window
 Fri, Apr 3 4:00 PM PDT to Tue, Apr 14 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring15Probs.pdf
 Problem answers
 Show

April 2015 Fun Round
An April Fool's event for 2015. NOTE: There was an error in the indices i and j for Problem 4 which has now been fixed. We apologize for the mistake.
 Type
 Monthly Contest (Rules)
 Contest window
 Wed, Apr 1 12:00 AM PDT to Wed, Apr 1 11:59 PM PDT
 Duration
 24 hours and 0 seconds
 Number of problems
 8
 Problem weights
 2.0, 1.0, 3.0, 4.0, 7.0, 11.0, 18.0, 29.0 (Total: 75.0)
 Problems file
 Tribute.pdf
 Problem answers
 Show
 More details
 Show

Contest 18
March Contest
 Type
 Monthly Contest (Rules)
 Contest window
 Sun, Mar 22 4:55 PM PDT to Sun, Mar 22 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO018.pdf
 Problem answers
 Show
 More details
 Show

Revenge 17
January Revenge Contest
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Jan 23 4:55 PM PST to Fri, Jan 23 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO017.pdf
 Problem answers
 Show
 More details
 Show

Contest 16
November Contest 2014
 Type
 Monthly Contest (Rules)
 Contest window
 Wed, Nov 19 4:55 PM PST to Wed, Nov 19 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO016.pdf
 Problem answers
 Show
 More details
 Show

OMO Fall 2014
Fall 2014 contest. As usual, teams of four submit answers to 30 problems over the span of about a week.
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Oct 17 4:00 PM PDT to Tue, Oct 28 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall14Probs.pdf
 Problem answers
 Show

Contest 15
September Contest 2014
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Sep 15 4:55 PM PDT to Mon, Sep 15 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO015.pdf
 Problem answers
 Show
 More details
 Show

Summer Contest 2014
The NIMO 2014 Summer Contest. As usual, 15 problems in 15 minutes, where problem N is worth N points.
 Type
 Summer Contest (Rules)
 Contest window
 Sat, Aug 23 4:57 PM PDT to Sat, Aug 23 5:17 PM PDT
 Duration
 15 minutes and 0 seconds
 Number of problems
 15
 Problem weights
 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 (Total: 120.0)
 Problems and answers
 Problems and answers
 Penalty per minute spent on correct problems
 1.0

Contest 14
May 2014 Contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, May 16 4:55 PM PDT to Fri, May 16 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO014.pdf
 Problem answers
 Show
 More details
 Show

OMO Spring 2014
The OMO contest for Spring 2014. 30 problems from April 4 to April 15 at 4PM PT / 7PM ET each day.
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Apr 4 4:00 PM PDT to Tue, Apr 15 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOSpring14Probs.pdf
 Problem answers
 Show

April Fools' 2014
Have fun! :)
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Mar 31 6:00 PM PDT to Tue, Apr 1 11:59 PM PDT
 Duration
 30 hours and 0 seconds
 Number of problems
 9
 Problem weights
 2.0, 3.0, 5.0, 7.0, 11.0, 13.0, 17.0, 19.0, 23.0 (Total: 100.0)
 Problems file
 Tragedy9.pdf
 Problem answers
 Show
 More details
 Show

Revenge 13
Due to server downtime, we are not able to access the studentsubmitted proposals for the February contest. We will just defer the studentwritten contest to the March monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Mar 24 4:55 PM PDT to Mon, Mar 24 5:45 PM PDT
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO013.pdf
 Problem answers
 Show
 More details
 Show

Contest 12
Due to server downtime, we are not able to access the studentsubmitted proposals for the February contest. We will just defer the studentwritten contest to the March monthly contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Mon, Feb 24 4:55 PM PST to Mon, Feb 24 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO012.pdf
 Problem answers
 Show
 More details
 Show

Contest 11
January 2014 contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Fri, Jan 31 4:55 PM PST to Fri, Jan 31 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO011.pdf
 Problem answers
 Show
 More details
 Show

2014 NIMO Winter Contest
The 2014 Winter Contest is, like its a predecessors, a proofbased contest for teams of up to four. Teams may communicate online, and type their solutions. The contest has a time limit of one hour. The remaining 30 minutes of the time period are to be used only for compiling and uploading solutions.
 Type
 Winter Contest (Rules)
 Contest window
 Wed, Jan 1 12:00 AM PST to Mon, Jan 13 11:59 PM PST
 Teams
 View Team
 Duration
 1 hour, 30 minutes and 0 seconds
 Number of problems
 8
 Problems file
 Problems.pdf
 Scores
 Scores are available! View your score here.

Contest 10
December 2013 contest.
 Type
 Monthly Contest (Rules)
 Contest window
 Tue, Dec 3 4:55 PM PST to Tue, Dec 3 5:45 PM PST
 Duration
 40 minutes and 0 seconds
 Number of problems
 8
 Problem weights
 5.0, 5.0, 6.0, 6.0, 7.0, 8.0, 9.0, 10.0 (Total: 56.0)
 Problems file
 NIMO010.pdf
 Problem answers
 Show
 More details
 Show

Revenge 9
The studentwritten contest. There will be eight questions to solve over 40 minutes. To participate, click the "Start/Continue Contest" link at the start of the contest window.

OMO Fall 2013
OMO contest for Fall 2013.
 Type
 OMO Contest (Rules)
 Contest window
 Fri, Oct 18 4:00 PM PDT to Tue, Oct 29 4:00 PM PDT
 Teams
 View Team
 Duration
 264 hours and 0 seconds
 Number of problems
 30
 Problems file
 OMOFall13Probs.pdf
 Problem answers
 Show

Contest 8
NIMO Monthly Contest for September 2013.

Summer Contest 2013
The NIMO 2013 Summer Contest. 15 problems, 15 minutes. Problem n is worth n points. Tiebreaking is done by highest problem solved. In the event that there is still a tie, a penalty equal to the sum of the number of minutes spent on each correctly answered problem will be used to break the tie.
 Type
 Summer Contest (Rules)
 Contest window
 Sat, Aug 10 5:00 PM PDT to Sat, Aug 10 5:25 PM PDT
 Duration
 15 minutes and 0 seconds
 Number of problems
 15
 Problem weights
 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 (Total: 120.0)
 Problems and answers
 Problems and answers
 Penalty per minute spent on correct problems
 1.0
Monthly Contest #7 (May 2013)
ProblemsApril Fools' 2013
Problems
USAYNO (see #9)
SolutionsMonthly Contest #6 (February 2013)
ProblemsMonthly Contest #5 (January 2013)
Problems2013 Winter Contest
Problems
SolutionsMonthly Contest #4 (December 2012)
ProblemsMonthly Contest #3 (November 2012)
ProblemsMonthly Contest #2 (October 2012)
ProblemsMonthly Contest #1 (September 2012)
Problems2012 Summer Contest
Problems
Solutions2012 Winter Contest
Problems
Solutions2011 Summer Contest
Problems
Solutions2011 Winter Contest
Problems
Solutions