import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;


public class Main {

    static PrintWriter pw;

    public static void main(String[] args) throws FileNotFoundException {
        Scanner in = new Scanner(new File("input.txt"));
        pw = new PrintWriter(new File("output.txt"));
        MyQueue queue = new MyQueue(100000);
        String command;
        int s;
        do {
            command = in.next();
            switch (command) {
                case "push":
                    queue.push(in.nextInt());
                    break;
                case "pop":
                    s = queue.pop(queue.size());
                    pw.println((s == -999999999) ? ("error") : (s));
                    break;
                case "front":
                    pw.println((queue.front(queue.size()) == -999999999) ? ("error") : queue.front(queue.size()));
                    break;
                case "size":
                    pw.println(queue.size());
                    break;
                case "clear":
                    queue.clear();
                    break;
                default:
                    queue.exit();
            }
        } while (!command.equals("exit"));

        in.close();
        pw.close();
    }

    static class MyQueue {
        int maxSize;
        int[] queArray;
        int front;
        int rear;
        int nItems;

        public MyQueue(int sizeQueue) {
            maxSize = sizeQueue;
            queArray = new int[maxSize];
            front = 0;
            rear = -1;
            nItems = 0;
        }

        public void push(int element) {
            if (rear == maxSize - 1) rear = -1;
            queArray[++rear] = element;
            nItems++;
            pw.println("ok");
        }

        public int pop(int size) {
            if (size != 0) {
                int temp = queArray[front++];
                if (front == maxSize) {
                    front = 0;
                    rear = -1;
                    nItems = 1;
                }
                nItems--;
                return temp;
            } else return -999999999;
        }

        public int front(int size) {
            if (size != 0) return (queArray[front]);
            else return -999999999;

        }

        public int size() {
            return nItems;
        }

        public void clear() {
            front = 0;
            rear = -1;
            nItems = 0;
            pw.println("ok");
        }

        public void exit() {
            pw.println("bye");
        }

    }

}