空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld
题目描述
Jichang Xueshe, the most important thing is persistence!
Jichang learned how to shoot from Feiwei, and succeeded three years later. When an arrow is shot, it can shoot through three view planes (front view, right view and top view) of a cube with side length N at the same time, and the coordinates of the view planes penetrated are the same. The unit cube (side length is 1) hit by the arrow will disappear immediately. Do you know how much volume is left in the cube after Jichang shoots the M arrow?
输入描述:
The first line is two integers N (1≤N≤100), M (0≤M≤N×N) , representing the side length of the cube and the number of times Jichangshoots. Next, there are M rows, each row contains two integers a, b (1≤a, b≤N), which are the two coordinate values of the view surface.
输出描述:
Output an integer, that is, the remaining volume of the cube.