#include<bits/stdc++.h>

using namespace std;
int jiecheng(int n) {
	if (n == 1) {
		return n;
	}
	return n * jiecheng(n - 1);
}

int main() {
	int n, sum = 0;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		sum += jiecheng(i);
	}
	cout << sum;
	return 0;
}