using System;

public class Program

{

    public static void Main()

    {

        var a = new MyClass();

        Console.WriteLine("Puzzle of 6 is = {0}", a.Puzzle(6));

        Console.ReadLine();

    }

     public class MyClass

    {

        public int Puzzle(int n)

        {

            var c = n;

            var result = 0;

​

            if (c == 1)

                return 1;

​

            result = Puzzle(c - 1) * c;

            return result;

        }

    }

}