#include <bits/stdc++.h>
using namespace std;

int main() {
	int a, b[999999], c = 0;
	cin >> a;
	for (int i = 1; i <= a; i++) {
		b[i] = 1;
		for (int j = 1; j <= i; j++) {
			b[i] *= j;
		}
		c += b[i];
	}
	cout << c;
	return 0;
}