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: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Deque;
 
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        final Deque<String> numbers = new ArrayDeque<String>(1000000);
 
        final int n = Integer.parseInt(reader.readLine());
 
        String line;
        for (int i = 0; i < n; ++i) {
            line = reader.readLine();
            if ('i' == line.charAt(0)) {
                numbers.offerFirst(line.substring(7));
 
            }else if ('F' == line.charAt(6)) {
                numbers.remove();
 
            } else if ('L' == line.charAt(6)) {
                numbers.removeLast();
 
            } else {
                numbers.removeFirstOccurrence(line.substring(7));
            }
        }
 
        final StringBuilder answer = new StringBuilder();
        answer.append(numbers.poll());
        while (numbers.size() != 0) {
            answer.append(" ").append(numbers.poll());
        }
 
        System.out.println(answer.toString());
    }
}