public static void Main()
Console.WriteLine("Please enter one number under 200000");
ulong number = ulong.Parse(Console.ReadLine());
if (number > 10000000000000)
Console.WriteLine(number + "! = " + ans);
Console.WriteLine("Would you like to run the program again? Type \"y\" if yes.");
string choice = Console.ReadLine();
if (choice == "y" || choice == "Y")