using System;

public class Zadacha2

{

    public static void Main()

    {

         int n = Convert.ToInt32(Console.ReadLine()); 

         int factorial = 1;

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

         {

             factorial *= factorialNumber; 

         }

         Console.WriteLine(factorial / 2);

    }

}