3 cpp

#include <iostream>
#include <deque>
using namespace std;
int main() {
    int n, llo, kk;
    deque <int> a;
    cin >> n;
    while (n--) {
        cin >> llo;
        if (llo==1) {
            cin >> kk;
            a.push_front(kk);
        } else if (llo==2) {
            cin >> kk;
            a.push_back(kk);
        } else if (llo==3) {
            kk=a.front();
            cout << kk << " ";
            a.pop_front();
        } else {
            kk=a.back();
            cout << kk << " ";
            a.pop_back();
        }
    }
    return 0;
}