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public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StreamTokenizer in = new StreamTokenizer(br);
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

        Deque<Integer> queue = new ArrayDeque<>();
        while (in.nextToken() != StreamTokenizer.TT_EOF) {
            int n = (int) in.nval;

            for (int i = 0; i < n; i++) {
                in.nextToken();
                int a = (int) in.nval;

                switch (a) {
                    case 1:
                        in.nextToken();
                        queue.add((int) in.nval);
                        break;
                    case 2:
                        if (queue.isEmpty()) {
                            out.println("ERR_CANNOT_POP");
                        } else {
                            queue.pollFirst();
                        }
                        break;
                    case 3:
                        if (queue.isEmpty()) {
                            out.println("ERR_CANNOT_QUERY");
                        } else {
                            out.println(queue.peekFirst());
                        }
                        break;
                    case 4:
                        out.println(queue.size());
                        break;
                    default:
                        break;
                }
            }
        }
        out.flush();
        out.close();
    }