http://codeforces.com/contest/34/problem/A
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=12&page=show_problem&problem=944
http://acmicpc-live-archive.uva.es/nuevoportal/data/problem.php?p=3912
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=193&page=show_problem&problem=1391
http://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=1318
http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=188&page=show_problem&problem=484
http://acmicpc-live-archive.uva.es/nuevoportal/data/problem.php?p=2158