## Description:

bobo has a permutation p

_{1},p

_{2},…,p

_{n} of 1,2,…,n.

Knowing m extra constraints of form p

_{ai}<p

_{bi}, bobo wanna count the number of different permutations modulo (10

^{9}+7).

It is guaranteed that there is at least one such permutation.

## Input:

The input consists of several tests. For each tests:

The first line contains n,m (1≤n≤40,0≤m≤20). Each of the following m lines contain 2 integers a

_{i},b

_{i}(1≤a

_{i},b

_{i}≤n).

## Output:

For each tests:

A single number denotes the number of permutations.

## Sample Input:

3 1
1 2
3 2
1 2
2 3

## Sample Output:

3
1