Problemas:
http://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=3900
http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3405
http://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=4367
http://acm.timus.ru/problem.aspx?space=1&num=1671
https://icpcarchive.ecs.baylor.edu/index.php?option=onlinejudge&page=show_problem&problem=2436
https://icpcarchive.ecs.baylor.edu/index.php?option=onlinejudge&page=show_problem&problem=4668
http://acm.timus.ru/problem.aspx?space=1&num=1651
Ranking:
http://ahmed-aly.com/Standings.jsp?ID=9282
