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#include<bits/stdc++.h>
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using namespace std;
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typedef long long ll;
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const ll N=2e5+10;
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ll n,m,x,y,i,j,a[N],f[N]={1};
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int main(){
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 cin>>n>>m;
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 for(i=1;i<=m;i++)cin>>x>>y,a[x]|=1<<y-1;
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 for(i=0;i<(1<<n);i++)
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  for(j=1;j<=n;j++)
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   if((a[j]&i)==a[j]&&!(i>>j-1&1))
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    f[i|(1<<j-1)]+=f[i];
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 cout<<f[(1<<n)-1];
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}