#include<fstream>
using namespace std;
int n,m,i,j,k,x,y,sum=0;
int a[21][21];
bool f[21];
void dfs(int k)
{
	int i;
	if (k==n+1)
	{
		sum++;
	}else{
		for (i=1;i<=n;i++)
			if ((f[i])and(a[k][i]!=-1))
			{
				f[i]=false;
				dfs(k+1);
				f[i]=true;
			}
	}
}
int main()
{
	for (i=1;i<=n;i++)
		for (j=1;j<=n;j++)
			a[i][j]=0;
	ifstream fin("examone.in");
	ofstream fout("examone.out");
	fin>>n>>m;
	if (m==0)
	{
		sum=1;
		for (i=1;i<=n;i++)
			sum=sum*i;
		fout<<sum;
		fin.close();
		fout.close();
		return 0;
	}
	for (i=1;i<=m;i++)
	{
		fin>>x>>y;
		a[x][y]=-1;
	}
	for (i=1;i<=n;i++)
		f[i]=true;
	dfs(1);
	fout<<sum;
	fin.close();
	fout.close();
	return 0;
}