hack:

4 6
4 2
4 4
1 1
1 4
1 1
1 3
1 3

-1

https://www.luogu.com.cn/blog/XTZORZ/solution-p2296

https://www.luogu.com.cn/blog/Diaosi114514/solution-p2296

https://www.luogu.com.cn/blog/yyy/solution-p2296

https://www.luogu.com.cn/blog/LitShone/solution-p2296

https://www.luogu.com.cn/blog/zhr666/solution-p2296

https://www.luogu.com.cn/blog/user36788/solution-p2296

https://www.luogu.com.cn/blog/ViXpop/solution-p2296

https://www.luogu.com.cn/blog/liuwenyao2003/p2296-xun-zhao-dao-lu-ti-xie

https://www.luogu.com.cn/blog/user56787/solution-p2296

https://www.luogu.com.cn/blog/caolaoshi/solution-p2296

https://www.luogu.com.cn/blog/Kesdiael3/solution-p2296

https://www.luogu.com.cn/blog/lcezych/solution-p2296

https://www.luogu.com.cn/blog/xky-666/solution-p2296

https://www.luogu.com.cn/blog/gouguodeyuanzhu/solution-p2296

https://www.luogu.com.cn/blog/BCZSX051117/solution-p2296

https://www.luogu.com.cn/blog/zqj/solution-p2296

https://www.luogu.com.cn/blog/hkxa/solution-p2296

https://www.luogu.com.cn/blog/aiyoupass/solution-p2296

https://www.luogu.com.cn/blog/code004/solution-p2296

https://www.luogu.com.cn/blog/37069/solution-p2296

https://www.luogu.com.cn/blog/user47136/solution-p2296

https://www.luogu.com.cn/blog/Lonely-Nepenthe/solution-p2296

https://www.luogu.com.cn/blog/user31984/solution-p2296

https://www.luogu.com.cn/blog/user53302/solution-p2296

https://www.luogu.com.cn/blog/user35804/solution-p2296

https://www.luogu.com.cn/blog/acxblogs/solution-p2296

https://www.luogu.com.cn/blog/user20695/solution-p2296

https://yizimiyuanxin.blog.luogu.org/solution-p2296

https://www.luogu.com.cn/blog/user31337/solution-p2296（freopen 删除后错误）

https://www.luogu.com.cn/blog/ylx/solution-p2296（freopen 删除后错误）

https://www.luogu.com.cn/blog/cowcowcow/solution-p2296

https://a-wnico-blog.blog.luogu.org/solution-p2296（CE，bits 打错）

https://www.luogu.com.cn/blog/user14941/solution-p2296（末尾 0.？+错误）