#include <bits/stdc++.h>
using namespace std;
int main(){
	long long t2=0,n;
	cin>>n;
	for (int i=1;i<=n;++i){
		long long t=1;
		for (int j=1;j<=i;++j){
			t*=j;
		}
	t2+=t;
	}
	cout<<t2;
	return 0 ;
}