## CCCHK '15 J3 - Queens can't attack me!

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Points: 5
Time limit: 1.0s
Memory limit: 256M

Problem type

Consider a square chessboard with cells and queens on the chessboard (Note: there are no other chess pieces besides the queens).

A queen can move vertically, horizontally or diagonally. As an example, consider the square chessboard with cells with one queen (denoted by the ♕ notation) in Figure 1 below. The cells that can be reached by the queen are marked with the ◯ notation. There are cells that cannot be reached by the queen.

Your task is to calculate the number of cells that are NOT reachable by any queens.

#### Input Specification

The first line contains two integers, and . Following are lines. Each line contains two integers and , representing the location of a queen, i.e., the queen is at th row and th column .

#### Output Specification

The number of cells that are not reachable by any queens.

#### Sample Input 1

6 1
4 3

#### Output for Sample Input 1

16

#### Sample Input 2

6 2
4 3
6 4

#### Output for Sample Input 2

9

#### Explanation

Figure 1 and Figure 2 correspond to Sample 1 and Sample 2, respectively.