SRYDANKA

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace song_encryption
{
    class Program
    {
        static void Main(string[] args)
        {
            bool invalid = false;
            String[] input;
            List<String> artist = new List<String>();
            List<String> song = new List<String>();
            do
            {
                input = Console.ReadLine().Split(':').ToArray();
                if (input[0] != "end")
                {
                    artist.Add(input[0]);
                    song.Add(input[1]);
                }
            } while (input[0] != "end");

            for (int j = 0; j < artist.Count; j++)
            {
                if (!(artist.ElementAt(j)[0] >= 'A' && artist.ElementAt(j)[0] <= 'Z'))
                {
                    Console.WriteLine("Invalid input!");
                }
                else
                {
                    for (int i = 1; i < artist.ElementAt(j).Length; i++)
                    {
                        if (!(artist.ElementAt(j)[i] >= 'a' && artist.ElementAt(j)[i] <= 'z' || artist.ElementAt(j)[i] == ' ' || artist.ElementAt(j)[i] == '\''))
                        {
                            invalid = true;
                        }
                    }
                    for (int i = 0; i < song.ElementAt(j).Length; i++)
                    {
                        if (!(song.ElementAt(j)[i] >= 'A' && song.ElementAt(j)[i] <= 'Z' || song.ElementAt(j)[i] == ' '))
                        {
                            invalid = true;
                        }
                    }
                    if (invalid == false)
                    {
                        int encryptionKey = artist.ElementAt(j).Length;
                        List<char> encryptedArtist = artist.ElementAt(j).ToList();
                        List<char> encryptedSong = song.ElementAt(j).ToList();

                        if ((encryptedArtist[0] + encryptionKey) <= 'Z')
                        {
                            encryptedArtist[0] = (char)(encryptedArtist[0] + encryptionKey);
                        }
                        else
                        {
                            int temp = (encryptedArtist[0] + encryptionKey) - 'Z';
                            encryptedArtist[0] = (char)('A' + temp);
                        }
                        for (int i = 1; i < encryptedArtist.Count; i++)
                        {
                            if (encryptedArtist.ElementAt(i) != ' ' && encryptedArtist.ElementAt(i) != '\'' && (encryptedArtist.ElementAt(i) + encryptionKey) <= 'z')
                            {
                                char element = encryptedArtist.ElementAt(i);
                                encryptedArtist.RemoveAt(i);
                                encryptedArtist.Insert(i,(char)(element + encryptionKey));
                            }
                            if (encryptedArtist.ElementAt(i) != ' ' && encryptedArtist[i] != '\'' && (encryptedArtist[i] + encryptionKey) > 'z')
                            {
                                char element = encryptedArtist.ElementAt(i);
                                int temp = (element + encryptionKey) - 'z';
                                encryptedArtist.RemoveAt(i);
                                encryptedArtist.Insert(i, (char)('a' + temp));
                            }
                        }
                        for (int i = 0; i < encryptedSong.Count; i++)
                        {
                            if (encryptedSong.ElementAt(i) != ' ' && (encryptedSong.ElementAt(i) + encryptionKey) <= 'Z')
                            {
                                char element = encryptedSong.ElementAt(i);
                                encryptedSong.RemoveAt(i);
                                encryptedSong.Insert(i, (char)(element + encryptionKey));
                                //encryptedSong[i] = (char)(encryptedSong[i] + encryptionKey);
                            }
                            else
                            {
                                char element = encryptedSong.ElementAt(i);
                                int temp = (element + encryptionKey) - 'Z';
                                encryptedSong.RemoveAt(i);
                                encryptedSong.Insert(i, (char)('A' + temp));

                                /*int temp = (encryptedSong[i] + encryptionKey) - 'Z';
                                encryptedSong[i] = (char)('A' + temp);*/
                            }

                        }
                        Console.Write("Successful encryption: ");
                        for(int i = 0; i < encryptedArtist.Count; i++)
                        {
                            Console.Write(encryptedArtist.ElementAt(i));
                        }
                        Console.Write("@");
                        for (int i = 0; i < encryptedSong.Count; i++)
                        {
                            Console.Write(encryptedSong.ElementAt(i));
                        }
                        Console.WriteLine();

                    }
                    else
                    {
                        invalid = false;
                        Console.WriteLine("Invalid input!");
                    }
                }
            }

        }
    }
}