static void Main(string[] args)
        {
            List <int> numbers = new List <int> {
                1, 4
            };

            System.Console.WriteLine("Size = " + numbers.Count);
            System.Console.WriteLine("numbers = " + numbers[1]);
            Book b = new Book();

            if (args.Length > 0)
            {
                Console.WriteLine($"Hello {args[0]}");
            }
            else
            {
                Console.WriteLine("Nothing!");
            }

            Book book1 = new Book();

            book1.AddGrade(5.8);
            book1.AddGrade(8.5);
            book1.AddGrade(4.2);
            System.Console.WriteLine("Average = " + book1.Average());
            System.Console.WriteLine("MaxGrade = " + book1.MaxGrade());
            System.Console.WriteLine("MinGrade = " + book1.MinGrade());
            System.Console.WriteLine("Book1 = " + book1.ToString());
        }