[StartCode]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp18
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List<int> numbers = new List<int>();
            bool beOpen = true;

            while (beOpen == true)
            {
                Console.WriteLine("Введите команду : ");
                string command = Console.ReadLine();

                switch (command)
                {
                    case "exit":
                        ExitProgram(ref beOpen);
                        break;
                    case "sum":
                        int sum = 0;

                        foreach(int number in numbers)
                        {
                            sum +=number;
                        }

                        Console.WriteLine(sum);
                        break;
                    default:
                        bool beNumber = int.TryParse(command, out var separateNumber);

                        if (beNumber == true)
                            numbers.Add(Convert.ToSByte(separateNumber));
                        else
                            Console.WriteLine("Ошибка ввода.");
                        break;
                }
            }
        }

        static void ExitProgram(ref bool beOpen)
        {
            beOpen = false;
        }
    }
}
[EndCode]