C++ :

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 2e5 + 10, MOD = 1e9 + 7;

typedef long long LL;

int n, m;
int p[N];
int l[N], r[N];

int find(int x)
{
    if (x != p[x])
        p[x] = find(p[x]);
    return p[x];
}

int main()
{
    cin >> n >> m;
    
    for (int i = 1; i <= n; ++ i )
        p[i] = i;
    
    while (m -- )
    {
        int a, b;
        cin >> a >> b;
        if (r[a] == b && l[b] == a)
            continue;
        if (r[a] || l[b] || find(a) == find(b))
        {
            cout << 0 << endl;
            return 0;
        }
        r[a] = b, l[b] = a;
        a = find(a), b = find(b);
        p[a] = b;
    }
    
    int res = 1, k = 1;
    for (int i = 1; i <= n; ++ i )
        if (find(i) == i)
            res = (LL)res * k ++ % MOD;
    
    cout << res << endl;
    
    return 0;
}