#include <iostream>
#include <string>
#include <deque>
int main() {
using namespace std; ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int t; cin >> t;
deque<int> dq;
while (t--) {
string cmd; cin >> cmd;
if (cmd == "push_front") {
int n; cin >> n;
dq.push_front(n);
}
else if (cmd == "push_back") {
int n; cin >> n;
dq.push_back(n);
}
else if (cmd == "pop_front") {
if (dq.empty()) {
cout << -1 << '\n';
}
else {
cout << dq.front() << '\n';
dq.pop_front();
}
}
else if (cmd == "pop_back") {
if (dq.empty()) {
cout << -1 << '\n';
}
else {
cout << dq.back() << '\n';
dq.pop_back();
}
}
else if (cmd == "size") {
cout << dq.size() << '\n';
}
else if (cmd == "empty") {
cout << dq.empty()<< '\n';
}
else if (cmd == "front") {
if (dq.empty()) {
cout << -1 << '\n';
}
else {
cout << dq.front() << '\n';
}
}
else if (cmd == "back") {
if (dq.empty()) {
cout << -1 << '\n';
}
else {
cout << dq.back() << '\n';
}
}
}
}
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