hack样例给的是：
in
```
5
1 24
1 25
1 20
3 23
3 23
```
out
```
22
```
by yutong_Seafloor @ 2023-11-29 18:18:07
@[yutong_Seafloor](/user/773747) 大哥您没换行啊
by baka24 @ 2024-01-06 10:49:24