### 问题 H: 小P上考场

[状态] [讨论版] [提交] [命题人:]

7 11 5 4
2 4 2
1 4 3
7 2 2
3 4 3
5 7 5
7 3 3
6 1 1
6 3 4
2 4 3
5 6 3
7 2 1

7


1<=n<=2500

1<=m<=6200

1<=a,b<=n