#include<iostream>
#include<cstdlib>
#include<cstdio>
using namespace std;
int n,m,xx,yy,q[21][21]={0};
unsigned long long answer=0;
bool w[21][21]={0},used[21]={0};
void dfs(int x);
int main()
{
	freopen ("examone.in","r",stdin);
	freopen ("examone.out","w",stdout);
	cin>>n>>m;
	xx=yy=0;
	for (int i=0;i<m;i++)
	{
		int a,b;
		cin>>a>>b;
		w[a][b]=true;
	}
	dfs(1);
	cout<<answer;
	return 0;
}

void dfs(int x)
{
	if (x==n+1)
	{
		/*for (int i=1;i<=n;i++)
		{
			for (int j=1;j<=n;j++)
			{
				cout<<q[i][j]<<' ';
			}
			cout<<endl;
		}
		cout<<endl;*/
		answer++;
		return;
	}
	else
	{
		for (int i=1;i<=n;i++)
		{
			if (used[i]||w[x][i])
				continue;
			used[i]=1;
			q[x][i]=1;
			x++;
			dfs(x);
			x--;
			q[x][i]=0;
			used[i]=0;
		}
	}
}