import java.util.*;
import java.io.*;
import java.lang.*;

class Node{
        int data;
        Node prev;
        Node next;
        Node(int d){
            data=d;
            prev=null;
            next=null;
        }
    }
  
class Test { 
    
    public static void main(String args[]) 
    { 
        Node head=new Node(10);
    	Node temp1=new Node(20);
    	Node temp2=new Node(30);
    	head.next=temp1;
    	temp1.prev=head;
    	temp1.next=temp2;
    	temp2.prev=temp1;
    	printlist(head);
    	
    } 
    
    public static void printlist(Node head){
        Node curr=head;
        while(curr!=null){
        System.out.print(curr.data+" ");
        curr=curr.next;
    }System.out.println();
    }
}