public static void Main(string[] args)
        {
            CustomStack <int> stack = new CustomStack <int>();

            stack.Push(4);
            stack.Push(5);
            stack.Push(6);
            stack.Push(7);

            foreach (var item in stack)
            {
                Console.WriteLine(item);
            }

            Console.WriteLine(stack.Contains(7));

            Console.WriteLine();

            while (stack.Count > 0)
            {
                Console.WriteLine(stack.Pop());
            }
        }