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

int main(){
	long long a = 0 , b = 0 , n = 0 , c = 0 , a1 = 1 , b1 = 0 ;
	cin >> n ;
	while ( a < n ) {
		a1 = 1 ;
		c++ ;
		for ( int i = 1 ; i <= c ; i++) {
			a1 *= i ;
		}
		a++ ;
		b1 += a1 ;
	} 
	cout << b1 ;
}