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.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    static final int INF = 1000000000;     
    
    public static void main(String[] args) throws Exception {                
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        List<Integer> res = new ArrayList<Integer>();
        for (int i = 0; i < n; ++i) {
            String op = input.next();
            if (op.equals("insert")) {
                int x = input.nextInt();
                res.add(0, x);
            } else if (op.equals("delete")) {
                int x = input.nextInt();
                if (res.contains(x)) res.remove(res.indexOf(x));
            } else if (op.equals("deleteFirst")) {
                if (res.size() > 0) res.remove(0);                
            } else if (op.equals("deleteLast")) {
                if (res.size() > 0) res.remove(res.size() - 1);
            }
        }
        if (res.size() > 0) {
            System.out.print(res.get(0));
            for (int i = 1; i < res.size(); ++i) System.out.print(" " + res.get(i));
        }        
        System.out.println("");
    }                
}