using System;

public class Program

{

    public static void Main()

    {

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

        int S=1;

        int S2=0;

        for (int i=1; i<=n; i++)

        {

            S=S*i;

            S2=S2+S;

        }

        Console.WriteLine(S2);

    }

}