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

struct node{
	unsigned int key;
	struct node *next;
	struct node *prev;
};

typedef struct node *NodePointer;

NodePointer nil;


NodePointer listSearch(int key){
	NodePointer cur = nil->next;
	while(cur != nil && cur->key != key){
		cur = cur->next;
	}
	return cur;
}


void init(){
	nil = malloc(sizeof(struct node));
	nil->next = nil;
	nil->prev = nil;
}


void printList(){
	NodePointer cur = nil->next;
	int isf = 1;
	while(1){
		if(cur == nil) break;
		if(isf == 0) printf(" ");
		printf("%d", cur->key);
		cur = cur->next;
		isf = 0;
	}
	printf("\n");
}


void deleteNode(NodePointer t){
	if(t == nil) return;
	t->prev->next = t->next;
	t->next->prev = t->prev;
	free(t);
}


void deleteFirst(){
	NodePointer t = nil->next;
	if(t==nil) return;
	deleteNode(t);
}


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


void delete(int key){
	deleteNode(listSearch(key));
}


void insert(int key){
	NodePointer x;
	x = malloc(sizeof(struct node));
	x->key = key;
	x->next = nil->next;
	nil->next->prev = x;
	nil->next = x;
	x->prev = nil;
}


int main(){
	int key, n, i;
	int size = 0;
	char com[20];
	int np = 0, nd = 0;
	scanf("%d", &n);
	init();
	for(i=0; i<n; i++){
		scanf("%s%d", com, &key);
		if(com[0] == 'i') {insert(key); np++; size++;}
		else if(com[0] == 'd')
		{
			if(strlen(com) > 6)
			{
				if(com[6] == 'F') deleteFirst();
				else if(com[6] == 'L') deleteLast();
			}
			else
			{
				delete(key); nd++;
			}
			size--;
		}
	}
	
	printList();
	return 0;
}