Problems

# Bishops

# Bishops

The bishop in chess is a piece that attacks all squares on the same diagonal (on both diagonals).

Shakhriyar placed **m** bishops on a chessboard of size **n** * **n**. Now he wants to count the number of squares that are not attacked by bishops. Help Shahriyar in this matter.

#### Input

First line contains two integers: the size **n** (**1** ≤ **n** ≤ `10`

) of a chessboard and the number of bishops ^{6}**m** (**1** ≤ **m** ≤ `10`

). Each of the next ^{5}**m** lines contains pair of integers: `r`

и _{i}`c`

(_{i}**1** ≤ `r`

, _{i}`c`

≤ _{i}**n**) - the numbers of row and column where the bishop number **i** is located. The bishops are numbered from **1** to **m**. All bishops are located on different squares.

#### Output

Print the number of squares not attacked by the bishops.

Input example #1

10 6 4 7 8 5 8 7 6 2 9 7 8 4

Output example #1

33

Input example #2

6 1 5 4

Output example #2

28

Input example #3

8 2 4 3 5 6

Output example #3

42