#include<bits/stdc++.h>
using namespace std;
int f(int n){
	if(n==1) return 1;
	else return f(n-1)+n;
}
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: wuzihang
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/