using System;

public class Program

{

    public static void Main()

    {

        var sum = 0;

            while (true)

            {

                Console.Write("Enter a number (or 'ok' to exit): ");

                var input = Console.ReadLine();

​

                if (input.ToLower() == "ok")

                    break;

​

                sum += Convert.ToInt32(input);

            }

            Console.WriteLine("Sum of all numbers is: " + sum);

    }

}