using System;

public class Program

{

    public static void Main()

    {

        string dico = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        string code = "E GHMYJVP ZEYZ TPYMW VR EYMZTTSL WLUW RSSTYI";

        int[] key = new int [3]{4,0,7};

​

        for (var k=0; k<26; k++)

        {

            int spaceCount = 0;

            key[1] = k;

            Console.Write(k + " : ");

            for (var i=0; i< code.Length; i++)

            {

                if (code[i] == ' ')

                {

                    Console.Write(' ');

                    spaceCount++;

                    continue;

                }

                int decalage = key[(i - spaceCount) % 3];

                int currentIndex = dico.IndexOf(code[i]);

                int newIndex = (currentIndex - decalage) % 26;

                if (newIndex < 0) newIndex = 26 + newIndex;

                try {

                    Console.Write(dico[newIndex]);

                }

                catch (Exception e)

                {

                    Console.WriteLine();

                    Console.WriteLine(newIndex + " : " + e.Message);

                }

            }

            Console.WriteLine();

        }

    }

}