输入：

1 10
PPPPPPPPPP

输出：

4

是不是4不重要，反正不可能是0

以下题解输出0

https://www.luogu.com.cn/blog/bilibiliboom/solution-p2704

https://www.luogu.com.cn/blog/Agemt-shadiao/noi2001-pao-bing-zhen-di

https://www.luogu.com.cn/blog/henryhe/solution-p2704

https://www.luogu.com.cn/blog/klc/solution-p2704

https://www.luogu.com.cn/blog/xcgzyouxiao/solution-p2704

只测了第一页的题解，后面几页可能还有