10. Multiply by 2

using System;

namespace MultiplyBy2
{
    class Program
    {
        static void Main(string[] args)
        {
            double spox = 0;
            spox: double num = double.Parse(Console.ReadLine());

            if (num >= 0)
            {
                spox = num;

                Console.WriteLine($"Result: {num * 2:F2}");
                goto spox;
            }
            else
            {
                Console.WriteLine("Negative number!");
            }

        }
    }
}