using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(encrypt("wqw","Hello World"));

    }

    public static string encrypt(string key, string message)

        {

            // TODO: Your own implementation!

            string result = "";

            if (string.IsNullOrEmpty(key))

            {

                key = "DCJ";

            }

            if (!string.IsNullOrEmpty(message))

            {

                var letras = message.ToCharArray();

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

                {

                    if (letras[i].ToString() == "a" || letras[i].ToString() == "A"

                      || letras[i].ToString() == "e" || letras[i].ToString() == "E"

                      || letras[i].ToString() == "i" || letras[i].ToString() == "I"

                      || letras[i].ToString() == "o" || letras[i].ToString() == "O"

                      || letras[i].ToString() == "u" || letras[i].ToString() == "U")

                    {

                        result += key + letras[i].ToString();

                    }

                    else

                    {

                        result += letras[i].ToString();

                    }

​

                }

            }

            return result;

        }

}