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 Ruby (judge verdict: Wrong Answer)

class Node
    attr_accessor :prev, :next, :key
    def initialize key
        @key = key
    end
end

class DoubllyLinkedList
    def initialize
        @head = nil
    end

    def insert key
        node = Node.new key
        node.next = @head
        @head.prev = node if @head
        @head = node 
    end

    def delete key
        head = @head
        until head.nil? || head.key == key
            head = head.next
        end
        unless head.nil?
            head.prev.next = head.next
            head.next.prev = head.prev if head.next
        end
    end

    def deleteFirst
        @head = @head.next
    end

    def deleteLast
        if @head
            head = @head
            until head.next.nil?
                head = head.next
            end
            head.prev.next = nil
        end
    end
    
    def keys
        arr = []
        head = @head
        while true
            arr << head.key
            break if head.next.nil?
            head = head.next
        end
        arr
    end
end

dll = DoubllyLinkedList.new
n = gets.to_i
n.times{
    line = gets.chomp.split
    case line[0]
    when "insert"
        dll.insert line[1]
    when "delete"
        dll.delete line[1]
    when "deleteFirst"
        dll.deleteFirst
    when "deleteLast"
        dll.deleteLast
    end
}
puts dll.keys.join(" ")