#include <bits/stdc++.h>
#define int int64_t
using namespace std;

int ms[3007][3007];

int32_t main()
{
    srand(time(NULL));
    ios_base::sync_with_stdio(0);
    int n;
    for (int i = 0; i < 3007; i ++)
        for (int j = 0; j < 3007; j ++)
            ms[i][j] = 0;
    cin >> n;
    for (int i = 0; i < n - 1; i ++)
    {
        int u, v;
        cin >> u >> v;
        ms[u][v] = 1;
    }
    vector<int> per;
    for (int i = 1; i <= n; i ++)
        per.push_back(i);
    int res = 0;
    do
    {
        bool ok = 1;
        map<int, int> pos;
        for (int i = 0; i < per.size(); i ++)
            pos[per[i]] = i;
        for (int i = 1; i <= n; i ++)
            for(int j = 1; j <= n; j ++)
            {
                if (i == j) continue;
                if (ms[i][j] && pos[i] > pos[j]) ok = 0;
            }
        if (ok)res++;
    }
    while (next_permutation(per.begin(), per.end()));
    cout << res;
}