链接：[http://codeforces.com/problemset/problem/793/B]
(http://codeforces.com/problemset/problem/369/C)

http://codeforces.com/problemset/problem/369/C

http://codeforces.com/problemset/problem/602/C

http://codeforces.com/problemset/problem/197/D

http://codeforces.com/group/xrTA2IaQje/contest/249572/problem/C