using System;

public class Program

{

    public static void Main()

    {

        //Get User Input

        Console.Write("Enter a number: ");

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

        Console.WriteLine("The factorial of {0}! is {1}",num,factorial(num));

    }

    private static int factorial(int num){

        int result;

        //Stop => Return to Upper Level

        if(num == 1){ 

            return 1;

        }else{

            //Call next level

            result = factorial(num-1) * num;

            //Return result

            return result;

        }

    }

}