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)

# 双方向連結リスト | アルゴリズムとデータ構造 | Aizu Online Judge http://is.gd/5CIlit
n = gets.chomp.to_i
doubleLinkedList = Array.new
n.times do
  command = gets.chomp
  if command == "deleteFirst" then
    doubleLinkedList.shift
  elsif command == "deleteLast" then
    doubleLinkedList.pop
  else
    command, x = command.split
    x = x.to_i
    if command == "insert" then
      doubleLinkedList.unshift(x)
    elsif command == "delete" then
      i = doubleLinkedList.index(x)
      doubleLinkedList.delete_at(i) if !i.nil?
    end
  end
end
puts doubleLinkedList.join(" ")