CSES Problem Set

Grid Paths

CSES - Grid PathsCSES - Grid Paths

 Time limit: 1.00 s Memory limit: 512 MB

Consider an $n \times n$ grid whose top-left square is $(1,1)$ and bottom-right square is $(n,n)$.

Your task is to move from the top-left square to the bottom-right square. On each step you may move one square right or down. In addition, there are $m$ traps in the grid. You cannot move to a square which has a trap.

What is the total number of possible paths?

Input

The first input line contains two integers $n$ and $m$: the size of the grid and the number of traps.

After this, there are $m$ lines that describe the traps. Each such line contains two integers $y$ and $x$: the location of a trap.

You can assume that there are no traps in the top-left and bottom-right square.

Output

Print the number of paths modulo $10^9+7$.

Constraints
• $1 \le n \le 10^6$
• $1 \le m \le 1000$
• $1 \le y,x \le n$
Example

Input:
3 1 2 2

Output:
2