import java.util.Iterator;


class DoubleIterator
    implements Iterator{
    
    private ListNode cursor,previous;

    public DoubleIterator(DoubleListNodeed list){
        cursor=list.getFirst();
    }

    public boolean hasNext(){
        return (cursor != null  && cursor.next !=null);
    }
    public Object next(){
        cursor=cursor.next;
        return cursor.data;
    }

    public void remove(){
      cursor.previous.next=cursor.next;
      cursor.next.previous=cursor.previous;
    }

}



public class DoubleListNodeed {
    private ListNode first;
    
    public ListNode getFirst(){
        return first;
    }
    
    Iterator listIterator(){
        return new DoubleIterator(this);
    }
}