class Program
    {
        static void Main(string[] args)
        {
            const string sumCommand = "sum";
            const string exitCommand = "exit";

            List<int> arrayNumbers = new List<int>();
            string userInput;
            bool isRunning = true;

            while (isRunning == true)
            {
                Console.Write("Введите команду: ");
                userInput = Console.ReadLine();

                switch (userInput)
                {
                    case sumCommand:
                        Summary(arrayNumbers);
                        break;

                    case exitCommand:
                        isRunning = false;
                        break;

                    default:
                        AddNumber(arrayNumbers,userInput);
                        break;
                }
            }
        }

        private static void AddNumber(List<int> arrayNumbers, string userInput)
        {
            if (int.TryParse(userInput, out int userNumber))
            {
                arrayNumbers.Add(userNumber);

                Console.WriteLine("Введено число " + userNumber);
            }
            else
            {
                Console.WriteLine("Неверный ввод команды!");
            }
        }

        private static void Summary(List<int> arrayNumbers)
        {
            int sum = 0;

            foreach (var number in arrayNumbers)
                sum += number;

            Console.WriteLine(sum);
        }
    }