using System;

namespace ConsoleApp23
{
    internal class Program
    {
        static void Main(string[] args)
        {
            const string CommandSum = "sum";
            const string CommandExit = "exit";

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

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

                if (userInput == CommandExit)
                {
                    isWork = false;
                }
                else if (userInput == CommandSum)
                {
                    int sum = 0;

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

                    Console.WriteLine(sum);
                }
                else
                {
                    int[] temporaryNumbers = new int[numbers.Length + 1];

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

                    temporaryNumbers[temporaryNumbers.Length - 1] = Convert.ToInt32(userInput);
                    numbers = temporaryNumbers;
                }
            }
        }
    }
}