YELLOW,
    GREEN
  }

  private abstract static class CountingSupplier<E> implements Supplier<E>, Serializable {
    int count;

    abstract E getImpl();

    @Override
    public E get() {
      count++;
      return getImpl();
    }
  }

  private static class QueueSupplier extends CountingSupplier<Queue<Integer>> {
    @Override
    /*