2ра задача

using System;
using System.Text.RegularExpressions;

namespace _02._Deciphering
{
    class Program
    {
        static void Main()
        {
            var firstLine = Console.ReadLine();
            var secondLine = Console.ReadLine().Split();

            var pattern = @"^[d-z{}|#]+$";

            if (Regex.IsMatch(firstLine, pattern))
            {
                var word = Regex.Match(firstLine, pattern).ToString().ToCharArray();
                for (int i = 0; i < word.Length; i++)
                {
                    var symbol = (char)(word[i] - 3);
                    word[i] = symbol;
                }
                var finalWord = new string(word);

                var result = finalWord.Replace(secondLine[0], secondLine[1]);
                Console.WriteLine(result);
            }
            else
            {
                Console.WriteLine("This is not the book you are looking for.");
            }
        }
    }
}