using System;

public class Program

{

    public static void Main()

    {

    int n;

         Console.WriteLine("Input n :");

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

         int S = 1;

         int i = 1;

         int A = 0;

         while ( i <= n )

         {

            S = S * i;

            i = i + 1;

            A = A + S;

            //Console.WriteLine(S);

            //Console.WriteLine(i);

         }

         Console.WriteLine(A);

    }

}