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 br = new BufferedReader(new InputStreamReader(System.in));

        int n = Integer.parseInt(br.readLine());
         
        Deque<Integer> list = new ArrayDeque<>();
        for(int i = 0; i < n; i++) {
            String cmd = br.readLine();
            if(cmd.charAt(0) == 'i') {
                list.addFirst(Integer.parseInt(cmd.substring(7)));
            }else if(cmd.charAt(6) == ' ') {
                list.remove(Integer.parseInt(cmd.substring(7)));
            }else if(cmd.charAt(6) == 'F') {
                list.removeFirst();
            }else {
                list.removeLast();
            }
        }
 
        StringBuilder sb = new StringBuilder();
        sb.append(list.removeFirst());
        while(!list.isEmpty()) {
            sb.append(" ").append(list.removeFirst());
        }
        System.out.println(sb);
    }
}