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.IOException;
import java.io.InputStreamReader;
import java.util.LinkedList;

public class Main {
	public static void main(String[] args) throws IOException {
		final LinkedList<String> list = new LinkedList<String>();
		runProcessing(list);
		printList(list);
	}
	
	public static void printList(LinkedList<String> list) {
		final StringBuilder result = new StringBuilder();
		final String lb = System.getProperty("line.separator");
		final int size = list.size()-1;
		
		int i = 0;
		for (String key : list) {
			result.append(key).append(i < size ? " " : lb);
			i++;
		}
		System.out.print(result.toString());
	}

	public static void runProcessing(final LinkedList<String> list) throws IOException {
		final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		final int n = Integer.parseInt(reader.readLine());
		
		for (int i = 0; i < n; i++) {
			final String[] command = reader.readLine().split(" ");
			
			if ("insert".equals(command[0])) {
				list.addFirst(command[1]);
				
			} else if ("delete".equals(command[0])) {
				list.remove(command[1]);
				
			} else if ("deleteFirst".equals(command[0])) {
				list.removeFirst();
				
			} else if ("deleteLast".equals(command[0])) {
				list.removeLast();
			}
			if ((i % 500000) == 0) System.gc();
		}
	}
}