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++14 (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin >> n;
	string com;
	int key;
	list <int> va;
	for(int i=0;i<n;i++){
		cin >> com;
		if(com=="insert"){
			cin >> key;
			va.push_front(key);
		}
		if(com=="deleteLast")
			va.pop_back();
		if(com=="deleteFirst")
			va.pop_front();
		if(com=="delete"){
			cin >> key;
			for(auto itr=va.begin();itr!=va.end();itr++)
				if(*itr==key){
					va.erase(itr);
					break;
				}
		}
	}
	for(auto itr=va.begin();itr!=va.end();++itr){
		cout << *itr;
		if(itr!=--va.end())
			cout << " ";
		else
			cout << endl;
	}
	return 0;
}