using System;

​

public class Program

{

    public static void Main()

    {

        Start:

            Console.Clear();

        Console.WriteLine("Please enter a postive, whole number.");

        string input = Console.ReadLine();

        ulong n;

        if (ulong.TryParse(input, out n))

        {

            ulong fact = 1;

            for (ulong i = 1; i <= n; i++)

            {

                fact *= i;

            }

​

            Console.WriteLine("" + n + "!= " + fact);

            {

                if (n >= 66)

                    Console.WriteLine("the number you picked is too high");

            }

​

            Console.WriteLine("would you like to run the program again? y/n");

            string choice = Console.ReadLine();

            if (choice == "y" || choice == "y")

                goto Start;

        }

        else

        {

            Console.WriteLine("Please make sure to enter a positive whole number");

            goto Start;

        }

    }

}