using System.Collections.Generic;
using System.Threading;

public class CoffeeMachine {

   public static Queue<byte[]> Input;
   public static Queue<byte[]> Output;

   static Thread Task;

   public static void SwitchOn()
   {
      Input = new Queue<byte[]>();
      Output = new Queue<byte[]>();
      Task = new Thread( new ThreadStart(Behaviour) );
      Task.Start();
   }

   public static void SwitchOff()
   {
      Task.Abort();
   }

   static void Behaviour()
   {
      const int price = 50;
      int amount = 0;
      while(true) {
         while(Input.Count == 0) Thread.Sleep(100);
         byte[] bytes = Input.Dequeue();
         int i = Convert.ByteArrayToInt(bytes);
         amount = amount+i;
         while (amount >= price) {
            Output.Enqueue(Convert.StringToByteArray("coffee"));
            amount = amount-price;
         }
      }
   }
}