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

int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		s=s+f(i);
	}
	cout<<s;

}
/**************************************************************
	Problem: 1148
	User: 15159808820
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/