Encrypt_the_Messages

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _04.Encrypt_the_Messages
{
    class Encrypt_the_Messages
    {
        static void Main(string[] args)
        {
            string messageInput = Console.ReadLine();
            int totalCount = 0;
            string messageDecrypt = string.Empty;
            int letters = 0;
            char specialCharacters=' ';
            while (messageInput != "end" && messageInput != "END")
            {
                messageInput = Console.ReadLine();
                if (messageInput!= "start" && messageInput!= "end" && (messageInput != "START" && messageInput != "END")
                    && messageInput != string.Empty)
                {
                    totalCount++;
                    foreach (var character in messageInput)
                    {
                        if (character >= 'a' && character <= 'm')
                        {
                            letters = (character + 13);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character > 'm' && character <= 'z')
                        {
                            letters = (character - 13);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character >= 'A' && character <= 'M')
                        {
                            letters = (character + 13);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character > 'M' && character <= 'Z')
                        {
                            letters = (character - 13);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character == ' ')
                        {
                            letters = (character + 11);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character == ',')
                        {
                            letters = (character - 7);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character == '.')
                        {
                            letters = (character - 8);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character == '?')
                        {
                            letters = (character - 28);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else if (character == '!')
                        {
                            letters = (character + 3);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        else
                        {
                            letters = (character);
                            specialCharacters = Convert.ToChar(letters);
                        }
                        messageDecrypt += specialCharacters;
                    }

                    //char[] reverseMessage = messageDecrypt.ToCharArray();
                    //Array.Reverse(reverseMessage);
                    //string realMessage = new string(reverseMessage);

                    //if (totalCount >= 1)
                    //{
                    //    //Console.WriteLine("Total number of messages: {0}", totalCount);
                    //    Console.WriteLine(realMessage);
                    //    messageDecrypt = string.Empty;
                    //}
                }
            }
            //if (totalCount == 0)
            //{
            //    Console.WriteLine("No messages sent.");
            //}


            char[] reverseMessage = messageDecrypt.ToCharArray();
            Array.Reverse(reverseMessage);
            string realMessage = new string(reverseMessage);
            if (totalCount == 0)
            {
                Console.WriteLine("No messages sent.");
            }
            else
            {
                Console.WriteLine("Total number of messages: {0}", totalCount);
                Console.WriteLine(realMessage);
            }
        }
    }
}