#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<algorithm>
#include<cmath>
#include<utility>
#include<cstdlib>
#include<iomanip>	//cout<<setiosflags(ios::fixed)<<setprecision(2);
#include<ctime> //double a=(double)clock();	cout<<a<<endl;
using namespace std;
inline int read()
{
	int x=0,ff=1;char ch=getchar();
	while(ch>'9'||ch<'0'){if(ch=='-')ff=-1; ch=getchar();}
	while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}
	return ff*x;
}
int N,M,t1,t2,limit,sta[22];
bool map[22][22];
long long f[22][(1<<20)+10],ans=0;
int main()
{
	freopen("arrange.in","r",stdin);
	freopen("arrange.out","w",stdout);
	N=read(),M=read();limit=(1<<N)-1;
	for(int i=1;i<=M;i++){
		t1=read(),t2=read();
		map[t1][t2]=1;
	}
	sta[1]=1;
	for(int i=2;i<=N;i++)
		sta[i]=sta[i-1]<<1;
	f[0][0]=1;
	for(int i=1;i<=N;i++)
		for(int j=0;j<=limit;j++)
			if(f[i-1][j])
				for(int k=1;k<=N;k++)
					if(!map[i][k])
						if((sta[k]&j)==0)
							f[i][sta[k]|j]+=f[i-1][j];
	for(int i=0;i<=limit;i++)
		ans+=f[N][i];
	cout<<ans<<endl;
	return 0;
}