#include<bits/stdc++.h>
using namespace std;
int main() {
	__int128_t n;
	double sum = 0, ans = 1;
	cin>>n;
	for (__int128_t i = 1; i <= n; i++) {
		ans*=i;
		sum+=ans;
	}
	printf("%.0lf", sum);
	return 0;
}