using System;

public class Program

{

    public static void Main()

    {

        string nullString = null;

        string emptyString = "";

        string stringWith255Characters = new String('x', 255);

        string stringWithMoreThan255Characters = new String('y', 255);

        Console.WriteLine(nullString?.Substring(0, 255) ?? "nullString");

        Console.WriteLine(emptyString?.Substring(0, 255) ?? "emptyString");

        Console.WriteLine(stringWith255Characters?.Substring(0, 255) ?? "stringWith255Characters");

        Console.WriteLine(stringWithMoreThan255Characters?.Substring(0, 255) ?? "stringWithMoreThan255Characters");

    }

}