static void Main(string[] args)
        {
            string message = encryptMessage("Hello world", 3);
            Console.WriteLine(message);
            Console.WriteLine(encryptMessage(message,-3));
        }

        public static string encryptMessage(string message, int key)
        {
            string encryptMessage = "";
            foreach (char c in message)
            {
                char uniCode = (char)(System.Convert.ToInt32(c) + key);
                encryptMessage += uniCode.ToString();
            }
            return encryptMessage;
        }