错误样例:
输入:
```cpp
20 9
0 100
43 72
24 32
79 80
52 82
57 74
31 58
3 12
29 50
54 57
9 87
36 38
2 15
49 85
65 81
59 97
81 98
47 98
4 75
66 89
```
输出:
```cpp
55
```
by Owen_codeisking @ 2018-09-11 22:20:22
tql
%%%
by sleepyNick @ 2018-09-11 22:42:29
tql
%%%
by zhenglier @ 2019-05-16 09:54:01
区间排序要放在离散化之前!!!
by 清平乐 @ 2020-08-26 20:45:40