[백준] 덱 10866

#include <bits/stdc++.h>
using namespace std;

int main (void){
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    deque<int> D;
    
    int n;
    cin >> n;
    while(n--){
        string cmd;
        cin >> cmd;
        
        if(cmd =="push_front"){
            int x;
            cin >> x;
            D.push_front(x);
        }
        else if(cmd == "push_back"){
            int x;
            cin >> x;
            D.push_back(x);
        }
        else if(cmd == "pop_front"){
            if(D.empty()) cout << -1<< "\n";
            else{
                cout << D.front()<< "\n";
                D.pop_front();
            }
            
        }
        else if(cmd == "pop_back"){
            if(D.empty()) cout << -1<< "\n";
            else{
                cout << D.back()<< "\n";
                D.pop_back();
            }
        }
        else if(cmd =="size") cout << D.size()<< "\n";
        else if(cmd =="empty") cout<< D.empty()<< "\n";
        else if(cmd =="front") {
            if(D.empty()) cout <<-1<< "\n";
            else cout<< D.front()<< "\n";
        }
        else {
            if(D.empty()) cout << -1<< "\n";
            else cout <<D.back()<< "\n";
        }
    
    }

    return 0;
}