using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Console.WriteLine(Linkify("This is a magic word.", "magic"));

        Console.WriteLine(Linkify("This is a <a href='/link.html'>magic</a> word.", "magic"));

        Console.WriteLine(Linkify("This is a <a href='/link.html'>crazy magic stuff</a> word.", "magic"));

        Console.WriteLine(Linkify("This is a normal word", "magic"));

    }

    private static string Linkify(string phrase, string word)

    {

        int wordIndex = phrase.IndexOf(word);

        int linkBeginIndex = phrase.IndexOf("<a href");

        int linkEndIndex = phrase.IndexOf("</a>");

​

        if(linkBeginIndex == -1 || !(wordIndex > linkBeginIndex && wordIndex < linkEndIndex))

        {

            phrase = phrase.Replace(word, String.Format("<a href='/link.html'>{0}</a>", word));

        }

        return phrase;

    }

}