using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("n=");

        int n = int.Parse(Console.ReadLine());

        double sum = 0;

        for ( int i=0;i<=n; i++)

        {

            sum = sum + i*(i+1);

        }

        Console.WriteLine("sum = " + sum);

    }

}