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: Time Limit Exceeded)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct node{
    struct node *prev;
    struct node *next;
    long key;
}Node;

Node *First;

void init(){
    First = (Node *)malloc(sizeof(Node));
    First->prev = First;
    First->next = First;
    First->key = -1;
}


void Insert(long x){
    Node *NewNode;
    NewNode = (Node *)malloc(sizeof(Node));
    NewNode->key = x;
    NewNode->next = First->next;
    NewNode->prev = First;
    NewNode->next->prev = NewNode;
    NewNode->prev->next = NewNode;
}

void DeleteFirst(void){
    Node *deleteP;
    deleteP = First->next;
    deleteP->next->prev = deleteP->prev;
    First->next = deleteP->next;
    free(deleteP);
}

void DeleteLast(void){
    Node *deleteP;
    deleteP = First->prev;
    deleteP->prev->next = deleteP->next;
    First->prev = deleteP->prev;
    free(deleteP);
}

void Delete(long x){
    Node *cur;
    cur = First->next;
    for (;;){
        if (cur->key == x){
            cur->prev->next = cur->next;
            cur->next->prev = cur->prev;
            free(cur);
            break;
        }
        cur = cur->next;
    }
}


int main(void){
    int n;
    char command[20];
    long x;
    int i;
    Node *printNode;

    init();
    
    scanf("%d", &n);
    for (i = 0; i < n; i++){
        scanf(" %s %ld", command, &x);
        
        if (strcmp(command, "insert") == 0){
            Insert(x);
        }
        if (strcmp(command, "delete") == 0){
            Delete(x);
        }
        if (strcmp(command, "deleteFirst") == 0){
            DeleteFirst();
        }
        if (strcmp(command, "deleteLast") == 0){
            DeleteLast();
        }
    }
    printNode = First->next;

    while (printNode->next->key != -1){
        printf("%ld ", printNode->key);
        printNode = printNode->next;
    }

    printf("%ld\n", printNode->key);

    return 0;
}