18_5

 class Program
    {
        //static string RandomString(int length)
        //{
        //    const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ;.,/'!?<>{}[]:+-_=АБВГДЕЁЖЗИКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯ";
        //    var random = new Random();
        //    return new string(Enumerable.Repeat(chars, length)
        //      .Select(s => s[random.Next(s.Length)]).ToArray());
        //}

        static string ReplaceEnglishWords(string text)
        {
            string text1 = Regex.Replace(text, "([A-Z]|[a-z])+", "...");
            return text1;
        }

        static void Main(string[] args)
        {
            StreamReader fin = new StreamReader("input.txt");
            string text = fin.ReadToEnd();
            fin.Close();
            //string text = RandomString(100);
            string replaceText = ReplaceEnglishWords(text);
            Console.WriteLine(text);
            Console.WriteLine(replaceText);
        }
    }