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

/**************************************************************
	Problem: 1019
	User: zzz
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/