using System;

​

/* 

Implement math operation "factorial" on a non-negative integer numbers using recursion and cover it by unit tests

  n! = n x(n-1)x(n-2)x..3x2x1 

     = n x (n-1)!

  0! = 1

*/

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var result = factorial(5); // 5 

        Console.WriteLine($"Result: {result}");

    }

}