UseYourChainsBuddy-2

using System;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
public class UseYourChainsBuddy
{
    public static void Main()
    {
        Console.SetIn(new StreamReader(Console.OpenStandardInput(8192)));

        var input = Console.ReadLine();
        var pattern = @"<p>(.*?)<\/p>";
        var regex = new Regex(pattern);
        var matches = regex.Matches(input);
        var output = new StringBuilder();
        var paragraph = "";

        foreach (Match match in matches)
        {
            paragraph+=($"{match.Groups[1]} ");
        }
        paragraph = Regex.Replace(paragraph, @"[^a-z0-9]+", " ");

        for (int i = 0; i < paragraph.Length; i++)
        {
            var ch = ' ';
            if (paragraph[i] >= 'a' && paragraph[i] <= 'm')
            {
                ch =(char)(paragraph[i] + 13);
                output.Append(ch);

            }
            else if ((int)paragraph[i] >= 110 && (int)paragraph[i] <= 122)
            {
                ch = (char)(paragraph[i] - 13);
                output.Append(ch);
            }
            else
            {
                output.Append(paragraph[i]);

            }
        }
        Console.WriteLine(output);

    }
}