using System;

internal static class Program
{
    private static void Main(string[] args)
    {
        string code = "W-17";
        Console.WriteLine(code.AsBookingLabel());
    }
}

internal static class BookingLabels
{
    public static string AsBookingLabel(this string code)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(code);
        return "Booking " + code;
    }
}