#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){
		if (key == cur->key){ return cur; }
		cur = cur->next;
	}
	return NULL;
}

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

void delete(int key){
	NodePointer t = listSearch(key);
	if (t == NULL)return;
	deleteNode(t);
}