import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.LinkedList;
import java.util.Queue;
import java.util.StringTokenizer;
public class Main {
public static void main(String[] args) throws IOException {
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int N = Integer.parseInt(br.readLine());
Queue<Integer> queue = new LinkedList<>();
StringBuilder sb = new StringBuilder();
int last = 0;
while (N-- > 0) {
StringTokenizer st = new StringTokenizer(br.readLine(), " ");
switch (st.nextToken()) {
case "push":
last = Integer.parseInt(st.nextToken());
queue.add(last);
break;
case "pop":
sb.append(queue.isEmpty() ? -1 : queue.poll()).append("\n");
break;
case "size":
sb.append(queue.size()).append("\n");
break;
case "empty":
sb.append((queue.isEmpty() ? 1 : 0)).append("\n");
break;
case "front":
sb.append(queue.isEmpty() ? -1 : queue.peek()).append("\n");
break;
case "back":
sb.append(queue.isEmpty() ? -1 : last).append("\n");
break;
}
}
bw.write(sb + "");
bw.flush();
bw.close();
}
}
