18258

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 {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
//		StringBuilder sb = new StringBuilder();

		int N = Integer.parseInt(br.readLine());
		int temp = -1;
		Queue<Integer> q = new LinkedList<>();
		for (int i = 0; i < N; i++) {
			StringTokenizer st = new StringTokenizer(br.readLine(), " ");
			switch (st.nextToken()) {
			case "push":
				temp = Integer.parseInt(st.nextToken());
				q.add(temp);
				break;
			case "pop":
				if (q.isEmpty())
					bw.write(-1 + "\n");
				else
					bw.write(q.poll() + "\n");
				break;
			case "size":
				bw.write(q.size() + "\n");
				break;
			case "empty":
				if (q.isEmpty())
					bw.write(1 + "\n");
				else
					bw.write(0 + "\n");
				break;
			case "front":
				if (q.isEmpty())
					bw.write(-1 + "\n");
				else
					bw.write(q.peek() + "\n");
				break;
			case "back":
				if (q.isEmpty())
					bw.write(-1 + "\n");
				else
					bw.write(temp + "\n");
			}
		}

		bw.flush();
		bw.close();
	}
}