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 C++ (judge verdict: Accepted)

#include <iostream>
#include <list>
#include <string>
using namespace std;

int main(){
  int n,key;
  string command;
  list<int> a;
  list<int>::iterator it;

  cin >> n;
  
  for(int i=0;i<n;i++){
    cin >> command;
    if(command=="deleteFirst")
      a.pop_front();
    else if(command=="deleteLast")
      a.pop_back();
    else{
      cin >> key;
      if(command=="insert")
	a.push_front(key);
      else for(it=a.begin();it!=a.end();it++) if(*it==key){
	    a.erase(it);
	    break;
	  }
    }
  }

  int i=0;
  for(it=a.begin();it!=a.end();it++){
    if(i++) cout << " ";
    cout << *it;
  }
  cout << endl;
}