#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	int a[105];
	a[1]=1;
	int f=1;
	for(int i=2;i<=n;i++)
	{
		a[i]=(a[i-1])+i;
		f+=a[i];
	}
	cout<<f;
	return 0;
}
/**************************************************************
	Problem: 1148
	User: chenkexin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/