[https://www.luogu.com.cn/problem/P5321](https://www.luogu.com.cn/problem/P5321) ~~当初出题人给我说:"其实这道题很简单的"~~ by 乙津梦 @ 2019-12-14 00:26:01
https://www.luogu.com.cn/problem/P5399 这个怎么样 by noip @ 2019-12-14 00:42:15