#include <bits/stdc++.h>
using namespace std;
int main(){
	long long n,sum_small=1,sum_all=1,a;
	cin >> n;
	for(int i =2;i<=n;i++){
		sum_small*=i;
		sum_all+=sum_small;
	}
	cout << sum_all;
	return 0;
}