using System;

public class Program

{

    public static void Main()

    {

        float alfa;

        float beta;

        string op;

        string res;

        Start:

        Console.WriteLine("Hello!\nPlease insert your first number!");

            alfa = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine("\nGreat!\nNow please select another!");

            beta = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine("\nThank you, we're almost done!\nWhat operation would you like to use?");

                Operation:

            op = Console.ReadLine();

        switch(op)

            {

                case "mult":

                    Console.WriteLine("\nYour answer is " + (alfa*beta) + ". Thank you!");

                        break;

                case "div":

                    Console.WriteLine("\nYour answer is " + (alfa/beta) + ". Thank you!");

                        break;

                case "add":

                    Console.WriteLine("\nYour answer is " + (alfa+beta) + ". Thank you!");

                        break;

                case "sub":

                    Console.WriteLine("\nYour answer is " + (alfa-beta) + ". Thank you!");

                        break;

                default:

                    Console.WriteLine("\nI'm sorry, I don't understand.\nPlease try again.");

                    goto Operation;

                        break;

            }

        Console.WriteLine("\nWould you like to calculate something else?");

            res = Console.ReadLine();

        if(res == "yes" || res == "y")

            {

                Console.WriteLine(" ");

                goto Start;

            }

    }

}