#include<iostream>
using namespace std;

int digui(int n);

int main(){
	int n=0,s=0;
	cin>>n;
	
	for(int i=1;i<=n;i++){
		
		s=s+digui(i);
	}
	cout<<s<<endl;
}

int digui(int n){
	
	if(n==1)
		return 1;
	else
		return n+digui(n-1);
}

/**************************************************************
	Problem: 1148
	User: admin
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/