#include<bits/stdc++.h>
using namespace std;
int n,s=0,i;
int f(int x){
	if(x==1) return 1;
	else
		return	f(x-1)+x;
} 
int main(){
	cin>>n;
	for(i=1;i<=n;i++){
		s+=f(i);
	}
	cout<<s; 
	return 0;
}
/**************************************************************
	Problem: 1148
	User: houshanglin
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/