import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;

public class Main {

  public static ArrayDeque<Integer> deque = new ArrayDeque<>();

  public static void process(String s) {

    String[] split = s.split(" ");

    if (split[0].equals("push_front")) {
      deque.addFirst(Integer.parseInt(split[1]));
    } else if (split[0].equals("push_back")) {
      deque.addLast(Integer.parseInt(split[1]));
    } else if (split[0].equals("pop_front")) {
      if (deque.size() == 0) {
        System.out.println(-1);
      } else {
        System.out.println(deque.pollFirst());
      }
    } else if (split[0].equals("pop_back")) {
      if (deque.size() == 0) {
        System.out.println(-1);
      } else {
        System.out.println(deque.pollLast());
      }
    } else if (split[0].equals("size")) {
      System.out.println(deque.size());
    } else if (split[0].equals("empty")) {
      if (deque.size() == 0) {
        System.out.println(1);
      } else {
        System.out.println(0);
      }
    } else if (split[0].equals("front")) {
      if (deque.size() == 0) {
        System.out.println(-1);
      } else {
        System.out.println(deque.peekFirst());
      }
    } else if (split[0].equals("back")) {
      if (deque.size() == 0) {
        System.out.println(-1);
      } else {
        System.out.println(deque.peekLast());
      }
    }

  }


  public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    int count = Integer.parseInt(br.readLine());

    for (int i = 0; i < count; i++) {
      process(br.readLine());
    }

  }

}