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

/**************************************************************
	Problem: 1148
	User: wangyousi
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/