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: Accepted)

def main
  n = gets.to_i
  linked_list = LinkedList.new

  n.times do
    command = gets.split
    if command[1]
      linked_list.send(command[0], command[1].to_i)
    else
      linked_list.send(command[0])
    end
  end

  linked_list.print
end

class LinkedList
  def initialize
    @keys = []
  end

  def insert(key)
    @keys.unshift(key)
  end

  def delete(key)
    index = @keys.find_index(key)
    @keys.delete_at(index) if index
  end

  def deleteFirst
    @keys.shift
  end

  def deleteLast
    @keys.pop
  end

  def print
    puts @keys.join(" ")
  end
end

main