#include <bits/stdc++.h>
using namespace std;
int y,sum=0;
int leijia(int q){
	if(q==0)return 0;
	return sum+q+leijia(q-1);
}
int main(){
	cin>>y;
	sum=sum+leijia(y);
	cout<<sum;
}

/**************************************************************
	Problem: 1002
	User: zhouhongyi
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/