#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,b=0;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        b+=f(i);
    }
    cout<<b;
    return 0;
}
/**************************************************************
	Problem: 1148
	User: wuyichen
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/