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

int main(){
	int n;
	cin >> n;
	long long ans = 0;
	for (int i = 1; i <= n; i++){
		long long sum = 1;
		for (int j = 1; j <= i; j++){
			sum*=j;
		}
		ans += sum;
	}
	cout << ans;
}