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.util.LinkedList;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int c = sc.nextInt();
        LinkedList<Integer> l = new LinkedList<>();
        for (int i = 0; i < c; i++) {
            String op = sc.next();
            switch (op) {
                case "insert":
                    l.addFirst(sc.nextInt());
                    break;
                case "delete":
                    l.removeFirstOccurrence(sc.nextInt());
                    break;
                case "deleteFirst":
                    l.removeFirst();
                    break;
                case "deleteLast":
                    l.removeLast();
                    break;
            }
        }
        for (int i = 0; i < l.size(); i++) {
            System.out.print(l.get(i));
            if (i != l.size() - 1) {
                System.out.print(" ");
            }
        }
    }
}