http://codeforces.com/contest/356/problem/A
http://codeforces.com/contest/459/problem/D
http://codeforces.com/contest/61/problem/E
http://codeforces.com/contest/380/problem/C
http://codeforces.com/contest/474/problem/F
http://codeforces.com/contest/292/problem/E
http://codeforces.com/contest/501/problem/D
http://codeforces.com/contest/220/problem/E
http://codeforces.com/contest/338/problem/E
http://codeforces.com/contest/19/problem/D