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++11 (judge verdict: Accepted)

#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string>
using namespace std;

typedef struct Node{
    int key;
    Node *prev, *next;
}Node;

Node* nil = (Node*)malloc(sizeof(Node));

void initialize(void){
    nil -> key = -1;
    nil -> prev = nil;
    nil -> next = nil;
}

void insert(int value){
    Node* n = (Node*)malloc(sizeof(Node));
    nil->next->prev = n;
    n->key = value;
    n->prev = nil;
    n->next = nil->next;
    nil->next = n;
}

void delete_(int value){
    Node* n = nil->next;
    while(1){
        if(n == nil){
            break;
        }
        if(n->key == value){
            Node* n_prev = n->prev;
            Node* n_next = n->next;
            n->prev->next = n_next;
            n->next->prev = n_prev;
            free(n);
            break;
        }
        n = n->next;
    }
}

void deleteFirst(){
    Node* n = nil->next;
    n->next->prev = nil;
    nil->next = n->next;
    free(n);
}

void deleteLast(){
    Node* n = nil->prev;
    n->prev->next = nil;
    nil->prev = n->prev;
    free(n);
}

void print_elements(){
    bool is_first = true;
    Node* n = nil->next;
    while(n != nil){
        if(is_first){
            is_first = false;
        }else{
            printf(" ");
        }
        printf("%d", n->key);
        n = n->next;
    }
    printf("\n");
}

int main(void){
    int n;
    scanf("%d", &n);
    initialize();
    
    for(int i = 0; i < n; i++){
        char s[20];
        int value;
        scanf("%s", s);
        string s_ = s;

        if(s_ == "insert"){
            scanf("%d", &value);
            insert(value);
        }else if(s_ == "delete"){
            scanf("%d", &value);
            delete_(value);
        }else if(s_ == "deleteFirst"){
            deleteFirst();
        }else if(s_ == "deleteLast"){
            deleteLast();
        }
    }
    print_elements();
}