UseYourChainsBuddy

using System;
using System.Collections.Generic;
using System.IO;
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 List<string>();

        foreach (Match  match in matches)
        {
            var textToConvert = match.Groups[1].Value;
            textToConvert = Regex.Replace(textToConvert,@"[^a-z0-9]+", " ");
            var textArr = textToConvert.Split(new char[] {' '}, StringSplitOptions.RemoveEmptyEntries);


            for (int i = 0; i < textArr.Length; i++)
            {
                var newWord = new Queue<char>();
                var word = textArr[i];

                for (int y = 0; y < word.Length; y++)
                {
                    if ((int)word[y] >= 97 && (int)word[y] <= 109)
                    {
                        var ch = (char)(((int)word[y]) + 13);
                        newWord.Enqueue(ch);

                    }
                    else if ((int)word[y] >= 110 && (int)word[y] <= 122)
                    {
                        var ch = (char)(((int)word[y]) - 13);
                        newWord.Enqueue(ch);
                    }
                    else
                    {
                        newWord.Enqueue(word[y]);

                    }
                }
                output.Add(string.Join("", newWord));
            }

        }
        Console.WriteLine(string.Join(" ",output));
    }
}