#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long a[105];
    a[1] = 1;
    a[2] = 3;
    int n;
    cin>>n;
    int c = 0;
    for(int i = 3;i<=n;i++)
    {
        a[i] = a[i-1] + i;
    }
    for(int i = 1;i<=n;i++)
    {
        c+=a[i];
    }
    cout<<c;
}
/**************************************************************
	Problem: 1148
	User: wuyichen
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/