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

public class Main {

	private static final int BIG_NUM  = 2000000000;
	private static final int MOD  = 1000000007;

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

		String input_str[] = new String[2];
		LinkedList<String> list = new LinkedList<String>();
		StringBuilder ans = new StringBuilder();

		try {
			int N = Integer.parseInt(br.readLine());

			for(int loop = 0; loop < N; loop++){
				input_str = br.readLine().split("\\s+");

				if(input_str[0].equals("insert")){
					list.addFirst(input_str[1]);
				}else if(input_str[0].equals("delete")){
					list.remove(input_str[1]);
				}else if(input_str[0].equals("deleteFirst")){
					list.removeFirst();
				}else if(input_str[0].equals("deleteLast")){
					list.removeLast();
				}
			}

			if(!list.isEmpty()){
				ans.append(list.getFirst());
				list.removeFirst();
			}
			while(!list.isEmpty()){
				ans.append(" ").append(list.getFirst());
				list.removeFirst();
			}

			System.out.print(ans.toString());

		} catch (NumberFormatException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}