#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int jiecheng(int x){
	int sum = 1;
	for(int i = 1 ;i <= x ;i++){
		sum *= i;
	}
	return (sum);
}
int main()
{
	int N;
	cin >> N;
	int sum = 0;
	for(int i = 1 ;i <= N ;i++){
		sum += jiecheng(i);
	}
	cout << sum;
	return 0;
}