Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in JAVA (judge verdict: WA: Presentation Error)

import java.io.*;
import java.util.ArrayDeque;
public class Main {
    public static void main(String[] args) throws IOException{
	BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
	int n = Integer.parseInt(reader.readLine());
	ArrayDeque<Integer> list = new ArrayDeque<Integer>();
	String input;
	for (int i = 0; i < n; i++) {
	    input  = reader.readLine();
	    if (input.equals("deleteFirst")) {
		list.removeFirst();
	    } else if (input.equals("deleteLast")) {
		list.removeLast();
	    } else {
		if (input.startsWith("insert")) {
		    list.addFirst(Integer.parseInt(input.substring(7)));
		} else if (input.startsWith("delete")) {
		    list.remove(Integer.parseInt(input.substring(7)));
		}
	    }
	}
	System.out.print(list.poll());
	for (int i = 0; i < list.size(); i++) {
	    System.out.print(" " + list.poll());
	}
    }
}