#include <iostream>
#include <string>
using namespace std;

const int MAX = (10000 + 1) * 2;

int head = MAX / 2, tail = MAX / 2;
int arr[MAX];

// stl 사용하지 않고 구현
void push_front(int num)
{
	arr[--head] = num;
}

void push_back(int num)
{
	arr[tail++] = num;
}

void pop_front(void)
{
	head++;
}

void pop_back(void)
{
	tail--;
}

int front(void)
{
	return arr[head];
}

int back(void)
{
	return arr[tail - 1];
}

int main(void)
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int N;
	cin >> N;

	for (int n = 0; n < N; n++)
	{
		string s;
		cin >> s;

		if (s == "push_front")
		{
			int num;
			cin >> num;

			push_front(num);
		}
		else if (s == "push_back")
		{
			int num;
			cin >> num;

			push_back(num);
		}
		else if (s == "pop_front")
		{
			if (head == tail)
				cout << -1 << "\n";
			else
			{
				cout << front() << "\n";
				pop_front();
			}
		}
		else if (s == "pop_back")
		{
			if (head == tail)
				cout << -1 << "\n";
			else
			{
				cout << back() << "\n";
				pop_back();
			}
		}
		else if (s == "size")
		{
			cout << tail - head << "\n";
		}
		else if (s == "empty")
		{
			bool flag = (head == tail);
			cout << flag << "\n";
		}
		else if (s == "front")
		{
			if (head == tail)
				cout << -1 << "\n";
			else
				cout << front() << "\n";
		}
		else
		{
			if (head == tail)
				cout << -1 << "\n";
			else
				cout << back() << "\n";
		}
	}
	return 0;
}