#include <cstdio>
#include <cstdlib>
using namespace std;
const int MAXN=21;
int N,M;
unsigned long long Ans=0;
int Pos[MAXN];
int Fuka[MAXN][MAXN];

inline bool Check(int k,int j)
{
	if(Fuka[k][j]) return false;
	for(int i=1;i<=N;i++) {if(Pos[i]==j) return false;}
	return true;
}

int main()
{
	freopen("examone.in","r",stdin);
	freopen("examone.out","w",stdout);
	scanf("%d %d\n",&N,&M);
	if(M==0)
	{
		Ans=1;
		for(int i=2;i<=N;i++)
			Ans*=i;
		printf("%lld\n",Ans);
		exit(0);
	}
	if(M==1)
	{
		Ans=1;
		for(int i=2;i<=N-1;i++)
			Ans*=i;
		Ans*=(N-1);
		printf("%lld\n",Ans);
		exit(0);
	}
	for(int i=1;i<=N;i++) 
	{
		for(int j=1;j<=N;j++) Fuka[i][j]=0;
		Pos[i]=0;
	}
	int a,b;
	for(int i=1;i<=M;i++)
	{
		scanf("%d %d\n",&a,&b);
		Fuka[a][b]=1;
	}
	int i=1,j=1;
	while(i<=N)
	{
		while(j<=N)
		{
			if(Check(i,j))
			{
				Pos[i]=j;
				j=1;
				break;
			}
			else j++;
		}
		if(Pos[i]==0)
		{
			if(i==1)
			{
				printf("%lld\n",Ans);
				exit(0);
			}
			else
			{
				i--;
				j=Pos[i]+1;
				Pos[i]=0;
				continue;
			}
		}
		if(i==N)
		{
			Ans++;
			j=Pos[i]+1;
			Pos[i]=0;
			continue;
		}
		i++;
	}
	return 0;
}