using System;

public class Program

{

    public static void Main()

    {

    start:

Console.Clear();

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

string input = Console.ReadLine();

ulong n;

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

{

ulong fact = 1;

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

{

fact = i * fact;

}

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

if (n > 65)

Console.WriteLine( "Please enter smaller number. ");

else if (n <= 65)

Console.WriteLine("Thank you for using my program");

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

string choice = Console.ReadLine();

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

goto start;

}

else

{Console.WriteLine("You miust enter a positivé whole number.");

goto start;

}

    }

}