hack：整张图都为强连通图的情况

5 5
1 2
2 3
3 4
4 5
5 1

被hack的题解：

https://www.luogu.com.cn/blog/275273/solution-p7251
https://www.luogu.com.cn/blog/246005/solution-p7251
https://www.luogu.com.cn/blog/came11ia/solution-p7251