import java.util.*;

public class DoublyLinkedList {
  private Node head;
  private Node tail;
  public DoublyLinkedList() {
    head=null;
    tail=null;
  }
 
  private class Node {
    String element;
    Node next;
    Node prev;
   
    public Node(String s) {
      element = s;
      next = null;
      prev = null;
    }
  }
 
  public int count() {
    Node cur=head;
    int c=0;
    while(cur!=null){
      c++;
      cur=cur.next;
    }
    return c;
  }
 
 
  public void addFirst(String element) {
    Node tmp = new Node(element);
    if(head != null ) {
      tmp.next=head;
      head.prev = tmp;
    }
    head = tmp;
    if(tail == null) {
      tail = tmp;
    }
   
  }
 
  public void clear(){
    head=null;
    tail=null;
  }
 
  public void insert_alpha(String element){
    Node cur=head;
    if(cur==null){
      if(cur.element.compare(element) > 0){
        Node tmp = new Node(element);
        tmp.next=cur;
        tmp.prev=cur.prev;
        cur.prev.next=tmp;
        cur.prev=tmp;
       
      }
      else{
        cur=cur.next;
      }
    }
  }
 
  public static void main(String a[]){
   
   
  }
}