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.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayDeque;

class Main {

	static ArrayDeque<String> queue = new ArrayDeque<String>();

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int n = Integer.parseInt(br.readLine());
		for (int i = 0; i < n; i++) {
			String order = br.readLine();
			if (order.contains("F")) {
				queue.poll();
			} else if (order.contains("L")) {
				queue.pollLast();
			} else if (order.contains("insert")) {
				queue.addFirst(order.replace("insert ", ""));
			} else {
				queue.removeFirstOccurrence(order.replace("delete ", ""));
			}
		}

		System.out.print(queue.poll());
		while (queue.isEmpty() != true) {
			System.out.print(" " + queue.poll());
		}
	}
}