public class SpinningDiskDevice
{
   private int lastInput;
   private int transitions;

   /**
      Constructs a spinning disk device.
   */
   public SpinningDiskDevice()
   {
      lastInput = 0;
      transitions = -1;
   }

   /**
      Processes a new input
      @param input 0 or 1
   */
   public void add(int input)
   {
      if(input != lastInput)
      {
        lastInput = input;
        transitions++;
      }
   }

   /**
      Gets the number of transitions observed since this
      device has been constructed.
   */
   public int getTransitions()
   {
      return transitions;
   }
}