#include<iostream>
using namespace std;
int a,s=0,m=1;
int main(){
	cin>>a; 
	for (int i=1;i<=a;i++){
		for (int j=1;j<=i;j++){
			m=m*j;
		}
	s=s+m;
	m=1;
	}
	cout<<s;
	return 0;
}