#include<iostream>

using namespace std;

struct Node
{
	int body;
	Node* next;
	Node* previous;
	Node()
	{
		body = 0;
		next = NULL;
	}
};

class Queue
{
	Node* head;
	Node* tail;
public:
	Queue()
	{
		this->head = NULL;
		this->tail = NULL;
	}
	Queue(const Queue& obj)
	{
		this->head = obj.head;
		this->tail = obj.tail;
	}
	void push( int element)
	{
		Node* link = new Node;
		link->body = element;
		if (head->next != NULL)
		{
			this->head = link;
			this->tail = link;
		}
		else
		{
			link->body = element;
			tail->next = link;
			link->previous = tail;
			tail = tail->next;
		}
	}
	int pop()
	{
		Node* link = tail;
		int el = link->body;
		tail = tail->previous;
	}
};