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

int main() {
    int n;
    cin >> n;

    vector<int> q;   // 큐 역할
    int front = 0;   // 앞 인덱스

    while(n--) {
        string cmd;
        cin >> cmd;

        if(cmd == "push") {
            int x;
            cin >> x;
            q.push_back(x);
        }
        else if(cmd == "pop") {
            if(front == q.size()) {
                cout << -1 << endl;
            } else {
                cout << q[front] << endl;
                front++;   // 앞에서 하나 제거
            }
        }
        else if(cmd == "size") {
            cout << q.size() - front << endl;
        }
        else if(cmd == "empty") {
            if(front == q.size()) cout << 1 << endl;
            else cout << 0 << endl;
        }
        else if(cmd == "front") {
            if(front == q.size()) cout << -1 << endl;
            else cout << q[front] << endl;
        }
        else if(cmd == "back") {
            if(front == q.size()) cout << -1 << endl;
            else cout << q[q.size() - 1] << endl;
        }
    }
}