(eval-when (:compile-toplevel :load-toplevel :execute)
  (defparameter OPT
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0)))
  #+swank (progn (ql:quickload '(:cl-debug-print :fiveam))
                 (shadow :run)
                 (use-package :fiveam)))
#+swank (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)

;; BEGIN_INSERTED_CONTENTS
(defstruct (queue (:constructor make-queue
                    (&optional list &aux (tail (last list)))))
  (list nil :type list)
  (tail nil :type (or null (cons t null))))

(declaim (inline enqueue))
(defun enqueue (obj queue)
  (symbol-macrolet ((list (queue-list queue))
                    (tail (queue-tail queue)))
    (if (null list)
        (setf tail (list obj)
              list tail)
        (setf (cdr tail) (list obj)
              tail (cdr tail))))
  queue)

(declaim (inline enqueue-front))
(defun enqueue-front (obj queue)
  (symbol-macrolet ((list (queue-list queue))
                    (tail (queue-tail queue)))
    (if (null list)
        (setf tail (list obj)
              list tail)
        (push obj list))
    queue))

(defun read-fixnum+ (&optional (in *standard-input*))
  (declare (optimize (speed 3) (safety 0) (debug 0)))
  (macrolet ((%read-byte ()
               `(the (unsigned-byte 8)
                     #+swank (char-code (read-char in nil #\Nul))
                     #-swank (sb-impl::ansi-stream-read-byte in nil #.(char-code #\Nul) nil))))
    (let ((result (loop (let ((byte (%read-byte)))
                          (cond ((<= 48 byte 57)
                                 (return (- byte 48)))
                                ((zerop byte) ; #\Nul
                                 (return-from read-fixnum+ 0)))))))
      (declare ((integer 0 #.most-positive-fixnum) result))
      (loop
        (let* ((byte (%read-byte)))
          (if (<= 48 byte 57)
              (setq result (+ (- byte 48) (the fixnum (* result 10))))
              (return nil))))
      result)))

(defmacro define-int-types (&rest bits)
  `(progn
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "UINT~A" b)) () '(unsigned-byte ,b))) bits)
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "INT~A" b)) () '(signed-byte ,b))) bits)))
(define-int-types 2 4 7 8 15 16 31 32 62 63 64)

(defmacro println (obj &optional (stream '*standard-output*))
  `(let ((*read-default-float-format* 'double-float))
     (prog1 (princ ,obj ,stream) (terpri ,stream))))

(defconstant +mod+ 1000000007)

;; Hauptteil

(defun main ()
  (declare #.OPT)
  (let* ((n (read))
         (queue (make-queue))
         (out (make-string-output-stream :element-type 'base-char)))
    (declare (uint31 n))
    (if (evenp n)
        (dotimes (i n)
          (if (evenp i)
              (enqueue (read-fixnum+) queue)
              (enqueue-front (read-fixnum+) queue)))
        (dotimes (i n)
          (if (oddp i)
              (enqueue (read-fixnum+) queue)
              (enqueue-front (read-fixnum+) queue))))
    (let ((i 0))
      (declare (uint31 i))
      (dolist (x (queue-list queue))
        (write (the uint31 x) :stream out)
        (incf i)
        (when (< i n)
          (write-char #\  out)))
      (write-line (get-output-stream-string out)))))

#-swank(main)


Measured memory_bytes: 28128