#include <bits/stdc++.h>
using namespace std;
int main() {
	long long n, s2 = 1, s1 = 0;
	cin >> n;
	for (long long i = 1; i <= n; i++) {
		s2 = s2 * i;
		s1 += s2;
	}
	cout << s1;
	return 0;
}

??? 必关！！！