Encrypted Message

using System;

namespace EncryptedMessage
{
    class Program
    {
        public static void Main(string[] args)
        {
            string startCommand = string.Empty;
            while (startCommand != "START" && startCommand != "start")
            {
                startCommand = Console.ReadLine();
            }

            string command = string.Empty;
            string reversedMessage = string.Empty;
            string encryptedMessage = string.Empty;
            int messagesCount = 0;
            int checkerForMessageCounter = 0;
            int letterCounter = 0;
            while (true)
            {
                command = Console.ReadLine();

                if (command != "END" && command != "end")
                {
                    //reversing the message first
                    for (int currentLetter = (command.Length - 1); currentLetter >= 0; currentLetter--)
                    {
                        char letter = command[currentLetter];

                        reversedMessage += letter;
                    }

                    //encrypting the message
                    for (int currentLetter = letterCounter; currentLetter < reversedMessage.Length; currentLetter++)
                    {
                        char letter = reversedMessage[currentLetter];

                        if (letter >= 'a' && letter <= 'm')
                        {
                            switch (letter)
                            {
                                    case 'a': encryptedMessage += 'n'; break;
                                    case 'b': encryptedMessage += 'o'; break;
                                    case 'c': encryptedMessage += 'p'; break;
                                    case 'd': encryptedMessage += 'q'; break;
                                    case 'e': encryptedMessage += 'r'; break;
                                    case 'f': encryptedMessage += 's'; break;
                                    case 'g': encryptedMessage += 't'; break;
                                    case 'h': encryptedMessage += 'u'; break;
                                    case 'i': encryptedMessage += 'v'; break;
                                    case 'j': encryptedMessage += 'w'; break;
                                    case 'k': encryptedMessage += 'x'; break;
                                    case 'l': encryptedMessage += 'y'; break;
                                    case 'm': encryptedMessage += 'z'; break;
                            }
                        }
                        else if (letter >= 'n' && letter <= 'z')
                        {
                            switch (letter)
                            {
                                    case 'n': encryptedMessage += 'a'; break;
                                    case 'o': encryptedMessage += 'b'; break;
                                    case 'p': encryptedMessage += 'c'; break;
                                    case 'q': encryptedMessage += 'd'; break;
                                    case 'r': encryptedMessage += 'e'; break;
                                    case 's': encryptedMessage += 'f'; break;
                                    case 't': encryptedMessage += 'g'; break;
                                    case 'u': encryptedMessage += 'h'; break;
                                    case 'v': encryptedMessage += 'i'; break;
                                    case 'w': encryptedMessage += 'j'; break;
                                    case 'x': encryptedMessage += 'k'; break;
                                    case 'y': encryptedMessage += 'l'; break;
                                    case 'z': encryptedMessage += 'm'; break;
                            }
                        }
                        else if (letter >= 'A' && letter <= 'M')
                        {
                            switch (letter)
                            {
                                    case 'A': encryptedMessage += 'N'; break;
                                    case 'B': encryptedMessage += 'O'; break;
                                    case 'C': encryptedMessage += 'P'; break;
                                    case 'D': encryptedMessage += 'Q'; break;
                                    case 'E': encryptedMessage += 'R'; break;
                                    case 'F': encryptedMessage += 'S'; break;
                                    case 'G': encryptedMessage += 'T'; break;
                                    case 'H': encryptedMessage += 'U'; break;
                                    case 'I': encryptedMessage += 'V'; break;
                                    case 'J': encryptedMessage += 'W'; break;
                                    case 'K': encryptedMessage += 'X'; break;
                                    case 'L': encryptedMessage += 'Y'; break;
                                    case 'M': encryptedMessage += 'Z'; break;
                            }
                        }
                        else if (letter >= 'N' && letter <= 'Z')
                        {
                            switch (letter)
                            {
                                    case 'N': encryptedMessage += 'A'; break;
                                    case 'O': encryptedMessage += 'B'; break;
                                    case 'P': encryptedMessage += 'C'; break;
                                    case 'Q': encryptedMessage += 'D'; break;
                                    case 'R': encryptedMessage += 'E'; break;
                                    case 'S': encryptedMessage += 'F'; break;
                                    case 'T': encryptedMessage += 'G'; break;
                                    case 'U': encryptedMessage += 'H'; break;
                                    case 'V': encryptedMessage += 'I'; break;
                                    case 'W': encryptedMessage += 'J'; break;
                                    case 'X': encryptedMessage += 'K'; break;
                                    case 'Y': encryptedMessage += 'L'; break;
                                    case 'Z': encryptedMessage += 'M'; break;
                            }
                        }
                        else if (letter == ' ')
                        {
                            encryptedMessage += '+';
                        }
                        else if (letter == ',')
                        {
                            encryptedMessage += '%';
                        }
                        else if (letter == '.')
                        {
                            encryptedMessage += '&';
                        }
                        else if (letter == '?')
                        {
                            encryptedMessage += '#';
                        }
                        else if (letter == '!')
                        {
                            encryptedMessage += '$';
                        }
                        else if (letter >= '0' && letter <= '9')
                        {
                            encryptedMessage += letter;
                        }
                    }

                    //getting to know where to start from in the previous for
                    for (int currentLetter = 0; currentLetter < command.Length; currentLetter++)
                    {
                        letterCounter++;
                        checkerForMessageCounter++;
                    }

                    //counting the messages
                    if (checkerForMessageCounter > 0)
                    {

                        encryptedMessage += "\n";
                        messagesCount++;
                        checkerForMessageCounter = 0;
                    }
                }
                else
                {
                    break;
                }
            }

            if (letterCounter > 0)
            {
                Console.WriteLine("Total number of messages: {0}", messagesCount);
                Console.WriteLine(encryptedMessage);
            }
            else
            {
                Console.WriteLine("No messages sent.");
            }

        }
    }
}