这道题的公式是啥，听说过，却忘了qwq

题目总版

@[xiezihan](/space/show?uid=219814) noip真题有
by 御坂美琴0502 @ 2019-09-16 20:32:19

@[弱小的蒟蒻](/space/show?uid=212902) # 求题号，求题号，求题号!
by xiezihan @ 2019-09-16 20:34:35

@[弱小的蒟蒻](/space/show?uid=212902) @[弱小的蒟蒻](/space/show?uid=212902) @[弱小的蒟蒻](/space/show?uid=212902)
by xiezihan @ 2019-09-16 20:37:38

$\frac{(n+1)(m+1)}{4}$
by Karry5307 @ 2019-09-16 20:38:42

@[Karry5307](/space/show?uid=60990) # **谢大佬，谢大佬，谢大佬**
by xiezihan @ 2019-09-16 20:40:24

![](https://cdn.luogu.com.cn/upload/image_hosting/0h9jferg.png)
by xiezihan @ 2019-09-16 20:43:04

@[Karry5307](/space/show?uid=60990)
by xiezihan @ 2019-09-16 20:43:12