#include "bits/stdc++.h"
using namespace std;
int main() {
	long long n;
	cin >> n;
	long long ans = 1, co[22] = {};
	for (long long i = 1; i <= n; i++) {
		int a;
		cin >> a;
		co[a]++;
		ans *= i;
	}
	for (int i = 1; i <= n; i++) {
		long long k = 1;
		for (long long j = 1; j <= co[i]; j++) {
			k *= j;
		}
		ans /= k;
	}
	cout << ans << endl;
}