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: Memory Limit Exceeded)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Deque;
import java.util.LinkedList;

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

		int n = Integer.parseInt(br.readLine());

		Deque<Integer> q = new LinkedList<Integer>();
		for (int i = 0; i < n; i++) {
			String[] op = br.readLine().split(" ");

			if ("insert".equals(op[0])) {
				q.offerFirst(Integer.parseInt(op[1]));
			} else if ("delete".equals(op[0])) {
				q.remove(Integer.parseInt(op[1]));
			} else if ("deleteFirst".equals(op[0])) {
				q.pollFirst();
			} else {
				q.pollLast();
			}
			if (i % 200000 == 0) {
				System.gc();
			}
		}

		System.out.print(q.poll());
		for (Integer s : q) {
			System.out.print(" " + s);
		}
		System.out.println();

		if (br != null) {
			br.close();
			br = null;
		}
	}
}