using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var a = Regex.Replace("fitzroy st", "\\w+ st$", "street");

        Console.WriteLine(a);

        var b = Regex.Replace("fitzroy st", "^(\\w+ )st$", "$1 street");

        Console.WriteLine(b);

        var c = Regex.Replace("fitzroy st", "(?<=\\w+ )st$", "street");

        Console.WriteLine(c);

        var d = Regex.Replace("some dark place called fitzroy st", "(\\w+ )+ st$", "street");

        Console.WriteLine(d);

        // 

    }

}