using System;

public class Program

{

    public static void Main()

    {

        double? x = 10.0;

        double? y = null;

        Console.WriteLine($"x = {x}");

        Console.WriteLine($"x ?? 5.5 = {x ?? 5.5}");

        Console.WriteLine($"y = {y}");

        Console.WriteLine($"y ?? 5.5 = {y ?? 5.5}");

    }

}