10866.txt

import java.io.*;
import java.util.*;

public class Main
{
	public static void main(String... args) throws Exception
	{
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		StringBuilder sb = new StringBuilder();
		
		Deque<Integer> deque = new ArrayDeque<>();
		int N = Integer.parseInt(in.readLine());
		
		while (N-- > 0)
		{
			int num = 0;
			
			StringTokenizer tt = new StringTokenizer(in.readLine());
			String cmd = tt.nextToken();
			
			if (tt.countTokens() >= 1)
				num = Integer.parseInt(tt.nextToken());
			
			if (cmd.equals("push_back"))
				deque.addLast(num);
			else if (cmd.equals("push_front"))
				deque.addFirst(num);
			else if (cmd.equals("front"))
			{
				if (deque.size() == 0)
					sb.append("-1\n");
				else
					sb.append(deque.peekFirst() + "\n");
			} else if (cmd.equals("back"))
			{
				if (deque.size() == 0)
					sb.append("-1\n");
				else
					sb.append(deque.peekLast() + "\n");
			} else if (cmd.equals("pop_front"))
			{
				if (deque.size() == 0)
					sb.append("-1\n");
				else
					sb.append(deque.pollFirst() + "\n");
			} else if (cmd.equals("pop_back"))
			{
				if (deque.size() == 0)
					sb.append("-1\n");
				else
					sb.append(deque.pollLast() + "\n");
			} else if (cmd.equals("size"))
				sb.append(deque.size() + "\n");
			else if (cmd.equals("empty"))
			{
				if (deque.isEmpty())
					sb.append("1\n");
				else
					sb.append("0\n");
			}
			
		}
		System.out.println(sb);
	}
}