#include <bits/stdc++.h>

using namespace std;

long long factorial(int n) {
    if (n == 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    long long s = 0;
    for (int i = 1; i <= 20; i++)
        s += factorial(i);

    cout << s << endl;
    return 0;
}