Deciphering_06.04.2019

using System;
using System.Linq;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Text;

namespace Deciphering_FinalExam_06._04._2019
{
    class Program
    {
        static void Main(string[] args)
        {
            char[] input = Console.ReadLine().ToCharArray();
            string[] secLine = Console.ReadLine().Split(" ").ToArray();
            string previous = secLine[0];
            string next = secLine[1];
            StringBuilder descrypt = new StringBuilder();

            for (int i = 0; i < input.Length; i++)
            {
                char symb = input[i];

                if ((symb >= 'd' && symb <= 'z') || symb == '{' || symb == '}' || symb == '|' || symb == '#' )
                {

                    int current = (int)symb - 3;
                    symb = (char)(current);
                    descrypt.Append(symb);
                }
                else
                {
                    Console.WriteLine("This is not the book you are looking for.");
                    break;
                }

            }
            string wordForDesc = descrypt.ToString();

            if (wordForDesc.Contains(previous))
            {
                descrypt.Replace(previous, next);
                Console.Write(string.Join(" ", descrypt));
            }
        }
    }
}