=LYDSY - 2570
wannafly模拟赛5C
cf #268(div1) B
cf #edu 33 D O(n)
UVA10641
https://www.nowcoder.com/acm/contest/30/C
https://www.nowcoder.com/acm/contest/73#question
https://vjudge.net/contest/221341#problem/F
http://poj.org/problem?id=3714 严格nlogn