[StartCode]
using System;

namespace ConsoleApp14
{
    internal class Program
    {
        static void Main(string[] args)
        {
            const string CommandSum = "sum";
            const string CommandExit = "exit";

            string userInput;
            int[] numbers = new int[0];
            bool isWork = true;

            while (isWork)
            {
                Console.WriteLine($"Введите команду : цифру , {CommandSum} или {CommandExit}.");
                userInput = Console.ReadLine();

                if (userInput == CommandSum)
                {
                    int sumNumber = 0;

                    for (int i = 0; i < numbers.Length; i++)
                    {
                        sumNumber += numbers[i];
                    }

                    Console.WriteLine(sumNumber);
                }
                else if (userInput == CommandExit)
                {
                    isWork = false;
                }
                else
                {
                    int[] temporaryArray = new int[numbers.Length + 1];
                    temporaryArray[numbers.Length] = Convert.ToInt32(userInput);

                    for (int i = 0; i < numbers.Length; i++)
                    {
                        temporaryArray[i] = numbers[i];
                    }

                    numbers = temporaryArray;
                }
            }
        }
    }
}
[EndCode]