#include <iostream>
using namespace std;
typedef long long ll;

int main()
{
    int n;
    cin >> n;
    ll fact[22];
    fact[0] = 1;
    for(int i = 1; i <= n; i++) fact[i] = fact[i - 1] * i;
    int b[22]{0};
    for(int i = 0; i < n; i++){
        int a;
        cin >> a;
        a--;
        b[a]++;
    }
    ll ans = fact[n];
    for(int i = 0; i < n; i++) ans /= fact[b[i]];
    cout << ans << endl;
}