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#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#include<bits/stdc++.h>
using namespace std;

vector<vector<long long>>dothi(100000000);
map<long long,long long>visited;

long long d=0;

void demduongdi(long long cur,long long end)
{
    visited[cur]=true;
    if(cur==end)
    {
        d++;
    }
    else
    {
        for(auto i=dothi[cur].begin();i!=dothi[cur].end();i++)
        {
            if(!visited[*i])
            {
                demduongdi(*i,end);
            }
        }
    }
    visited[cur]=false;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    #ifndef ONLINE_JUDGE
    freopen("input.inp","r",stdin);
    freopen("output.out","w",stdout);
    #else
    #endif
    long long n,m;
    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        long long x,y;
        cin>>x>>y;
        dothi[x].push_back(y);
    }
    for(int i=1;i<=n;i++)
    {
        visited[i]=false;
    }
    demduongdi(1,n);
    cout<<d;
    return 0;
}