[백준 10866] 덱

import java.util.ArrayList;
import java.util.Scanner;

class Dequeue {
	ArrayList<Integer> dequeue;
	int front = 0;
	int back=0;

	public Dequeue() {
		dequeue = new ArrayList<Integer>();
	}

	public void push_front(int X) {
		dequeue.add(front, X);
		back++;
	}

	public void push_back(int X) {
		dequeue.add(back, X);
		back++;
	}

	public int pop_front() {
		if (dequeue.size() < 1) {
			return -1;
		} else {
			back--;
			return dequeue.remove(front);
		}
	}

	public int pop_back() {
		if (dequeue.size() < 1) {
			return -1;
		} else {
			return dequeue.remove(--back);
		}
	}

	public int size() {
		return this.dequeue.size();
	}

	public int empty() {
		if (dequeue.size() < 1) {
			return 1;
		} else {
			return 0;
		}
	}

	public int front() {
		if (dequeue.size() < 1) {
			return -1;
		} else {
			return dequeue.get(front);
			
		}
	}

	public int back() {
		if (dequeue.size() < 1) {
			return -1;
		} else {
			return dequeue.get(back-1);
		}
	}
}

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int N = in.nextInt();
		Dequeue dequeue = new Dequeue();

		for (int i = 0; i < N; i++) {
			String command = in.next();
			if (command.equals("push_front")) {
				int X = in.nextInt();
				dequeue.push_front(X);

			} else if (command.equals("push_back")) {
				int X = in.nextInt();
				dequeue.push_back(X);
				
			} else if (command.equals("pop_front")) {
				System.out.println(dequeue.pop_front());

			} else if (command.equals("pop_back")) {
				System.out.println(dequeue.pop_back());

			} else if (command.equals("size")) {
				System.out.println(dequeue.size());

			} else if (command.equals("empty")) {
				System.out.println(dequeue.empty());

			} else if (command.equals("front")) {
				System.out.println(dequeue.front());

			} else if (command.equals("back")) {
				System.out.println(dequeue.back());

			} else {
				System.out.println("나가리");
			}
		}
	}
}