private static string DecodeMessage(string[] lines)
{
    List<string> list= new List<string>();
    foreach (var line in lines)
    {
        foreach (var word in line.Split(' '))
        {
            if (Char.IsUpper(word[0]))
                list.Add(word);
        }
    }
    list.Reverse();
    return string.Join(" ", list);
}