// 想定解
#include <cassert>
#include <iostream>
#include <map>
#include <vector>
using namespace std;

int main() {
    int N;
    cin >> N;
    assert(1 <= N and N <= 20);

    long long ret = 1;
    for (int i = 1; i <= N; ++i) ret *= i;
    map<int, int> counter;

    vector<int> A(N);
    for (int i = 0; i < N; ++i) {
        cin >> A[i];
        assert(1 <= A[i] and A[i] <= N);
        counter[A[i]]++;
    }

    for (auto [a, num_a] : counter) {
        for (int i = 1; i <= num_a; ++i) ret /= i;
    }
    cout << ret << '\n';
}