using System;

public class Program

{

    public static void Main()

    {

            {

        start:

        Console.WriteLine("What would you like to calculate the factorial of?");

        string ans = Console.ReadLine();

        ulong ans1;

        if (ulong.TryParse(ans, out ans1));

            ulong fact = 1;

            for(ulong i = 1;i <=ans1;i++)

                {fact *= i;}

            Console.WriteLine(ans1+"! = " +fact);

             Console.WriteLine("Do you want to restart? Please Enter Yes or No.");

                string answer = Console.ReadLine();

                if (answer == "Yes" || answer == "yes")

                {

                    Console.Clear();

                    goto start;

                }

        }

        }

​

​

}