#include<bits/stdc++.h>
using namespace std;
long long n;
long long ans;
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
    	int g=1;
    	for(int j=1;j<=i;j++){
    		g*=j;
		}
		ans+=g;
	}
	cout<<ans<<endl;
	return 0;
}
/**************************************************************
	Problem: 1019
	User: zengdongxin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/