using System;

​

​

public class Program

{

    private string CaesarCypher(string value, int shift)

    {

        char[] buffer = value.ToCharArray();

        for (int i = 0; i < buffer.Length; i++)

        {

            // Letter.

            char letter = buffer[i];

            if (Char.IsLetter(letter))

            {

                bool isLower = Char.IsLower(letter);

​

                // Add shift 

                letter = (char)(letter + shift);

​

                // Subtract 26 on overflow.

                // Add 26 on underflow.

                if (isLower)

                {

                    if (letter > 'z')

                        letter = (char) (letter - 26);

                    else if (letter < 'a')

                        letter = (char) (letter + 26);

                }

                else

                {

                    if (letter > 'Z')

                        letter = (char)(letter - 26);

                    else if (letter < 'A')

                        letter = (char)(letter + 26);

                }

            }

​

            // Store.

            buffer[i] = letter;

        }

        return new string(buffer);

    }

    public void Main()

    {

        string secretMessage = @"STGML MK

========

​

Ow sjw s yjgmh gx .FWL vwnwdghwjk ozg sjw kauc sfv lajwv gx klsjlafy Nakmsd Klmvag, ujwslafy s fwo hjgbwul sfv jmffafy al, bmkl lg lwkl kaehdw ugvw gj ljq gml ksehdwk xjge glzwj vwnwdghwjk.  

​

Lzak lggd osk afkhajwv tq zllh://bkxavvdw.fwl, ozauz ak bmkl sowkgew.

​

Ax qgm sjw aflwjwklwv af ogjcafy gf .FWL Xavvdw hdwskw kwfv qgmj jwkmew sfv dafck lg s ugmhdw gx qgmj twkl xavvdwk lg vglfwlxavvdw sl wflwuzkgdmlagfk vgl uge.  Lzw egkl aehjwkkanw xavvdw oadd ywl lzw bgt.

​

WFLwuz Kgdmlagfk

zllh://ooo.wflwuzkgdmlagfk.uge";

        string notSoSecretMessage = CaesarCypher(secretMessage, -18);

        Console.WriteLine(notSoSecretMessage);

    }

}