SemanticHTML

using System;
using System.Text.RegularExpressions;

class Semantic
{
    static void Main()
    {
        var openTagRegex = new Regex(@"<div.*?((?:id|class)\s*=\s*""(\w+?)"").*?>");
        var closeTagRegex = new Regex(@"<\/div>(\s*<!--\s*(\w+?)\s*-->)");

        string input;
        while ((input = Console.ReadLine()) != "END")
        {
            var output = input;

            //modify opening tags
            var match = openTagRegex.Match(input);
            if (match.Success)
            {
                output = input.Replace("div", match.Groups[2].Value);
                output = output.Replace(match.Groups[1].Value, "");
                output = Regex.Replace(output, @"\s+>", ">");
                output = Regex.Replace(output, @"\s+", " ");
            }

            //closing tags
            match = closeTagRegex.Match(input);
            if (match.Success)
            {
                output = output.Replace(match.Groups[1].Value, "");
                output = output.Replace("div", match.Groups[2].Value);
            }

            Console.WriteLine(output);
        }
    }
}