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

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

Node *nil;

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

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


void deleteNode(Node *d){
	if(d==nil)return;
	d->prev->next=d->next;
	d->next->prev=d->prev;
	free(d);
}

void deleteKey(int key){
	Node *now=nil->next;
	while(now!=nil && now->key!=key){
		now=now->next;
	}
	deleteNode(now);
}




void deleteFirst(){
	deleteNode(nil->next);
}

void deleteLast(){
	deleteNode(nil->prev);
}



int main(void)
{
	int i,n,key,j=0;
	char order[12];
	Node *now;
	
	
	scanf("%d",&n);
	init();
	
	for(i=0;i<n;i++){
		scanf("%s %d",order,&key);
		if(order[0]=='i')insert(key);
		else if(order[0]=='d'){
			if(order[6]=='F')deleteFirst();
			else if(order[6]=='L')deleteLast();
			else deleteKey(key);
		}
	}
	
	now=nil->next;
	while(1){
		if(now==nil)break;
		if(j>0)printf(" ");
		printf("%d",now->key);
		now=now->next;
		j++;
	}
	printf("\n");
	return 0;
}