#include<bits/stdc++.h>
using namespace std;
int f(int n)
{
	int r;
	if(n==1)
	{
		r=1;
	}
	else
	{
		r=f(n-1)+n;
	}
	return r;
}
int main()
{
	int n;
	cin>>n;
	int h=0;
	for(int i=1;i<=n;i++)
	{
		h+=f(i);
	}
	cout<<h;
	return 0;
}
/**************************************************************
	Problem: 1148
	User: chenkexin
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/