(eval-when (:compile-toplevel :load-toplevel :execute)
  (sb-int:defconstant-eqx OPT
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0))
    #'equal)
  #+swank (ql:quickload '(:cl-debug-print :fiveam) :silent t)
  #-swank (set-dispatch-macro-character
           ;; enclose the form with VALUES to avoid being captured by LOOP macro
           #\# #\> (lambda (s c p) (declare (ignore c p)) `(values ,(read s nil nil t)))))
#+swank (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)
#-swank (disable-debugger) ; for CS Academy

;; BEGIN_INSERTED_CONTENTS
(macrolet ((def (name fname)
             `(define-modify-macro ,name (new-value) ,fname)))
  (def minf min)
  (def maxf max)
  (def mulf *)
  (def divf /)
  (def iorf logior)
  (def xorf logxor)
  (def andf logand))

(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  "NOTE: cannot read -2^62"
  (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* ((minus nil)
           (result (loop (let ((byte (%read-byte)))
                           (cond ((<= 48 byte 57)
                                  (return (- byte 48)))
                                 ((zerop byte) ; #\Nul
                                  (error "Read EOF or #\Nul."))
                                 ((= byte #.(char-code #\-))
                                  (setf minus t)))))))
      (declare ((integer 0 #.most-positive-fixnum) result))
      (loop
        (let* ((byte (%read-byte)))
          (if (<= 48 byte 57)
              (setq result (+ (- byte 48)
                              (* 10 (the (integer 0 #.(floor most-positive-fixnum 10))
                                         result))))
              (return (if minus (- result) result))))))))

(defmacro dbg (&rest forms)
  #+swank
  (if (= (length forms) 1)
      `(format *error-output* "~A => ~A~%" ',(car forms) ,(car forms))
      `(format *error-output* "~A => ~A~%" ',forms `(,,@forms)))
  #-swank (declare (ignore forms)))

(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)

(declaim (inline println))
(defun println (obj &optional (stream *standard-output*))
  (let ((*read-default-float-format* 'double-float))
    (prog1 (princ obj stream) (terpri stream))))

(defconstant +mod+ 1000000007)

;;;
;;; Body
;;;

(declaim (inline solve))
(defun solve (n xs ys cumul-xs cumul-ys l-num init-dir end-dir)
  (dbg n l-num init-dir end-dir)
  (let* ((r-num (- n l-num))
         (min-lap (min l-num r-num))
         (l-lap (if (and (eq init-dir :left)
                         (eq end-dir :left))
                    (+ min-lap 1)
                    min-lap))
         (r-lap (if (and (eq init-dir :right)
                         (eq end-dir :right))
                    (+ min-lap 1)
                    min-lap))
         (res 0))
    (declare (fixnum r-num min-lap l-lap r-lap res))
    (when (or (> l-lap l-num) (> r-lap r-num))
      (return-from solve 0))
    (incf res (* 2 (- (aref cumul-xs l-num)
                      (aref cumul-xs (- l-num l-lap)))))
    (incf res (* 2 (- (aref cumul-ys r-num)
                      (aref cumul-ys (- r-num r-lap)))))
    (if (eq end-dir :left)
        (decf res (aref xs l-num))
        (decf res (aref ys r-num)))
    res))

(defun main ()
  (let* ((len (read))
         (n (read))
         (xs (make-array (+ n 1) :element-type 'uint31))
         (ys (make-array (+ n 1) :element-type 'uint31))
         (cumul-xs (make-array (+ n 1) :element-type 'uint62))
         (cumul-ys (make-array (+ n 1) :element-type 'uint62))
         (res 0))
    (declare (uint62 len n res))
    (dotimes (i n)
      (let* ((x (read-fixnum))
             (y (- len x)))
        (setf (aref xs (+ i 1)) x
              (aref ys (- n i)) y)))
    (dotimes (i n)
      (setf (aref cumul-xs (+ i 1))
            (+ (aref cumul-xs i) (aref xs (+ i 1)))
            (aref cumul-ys (+ i 1))
            (+ (aref cumul-ys i) (aref ys (+ i 1)))))
    (loop
      for l-num from 0 to n
      do (maxf res (solve n xs ys cumul-xs cumul-ys l-num :left :left))
         (maxf res (solve n xs ys cumul-xs cumul-ys l-num :left :right))
         (maxf res (solve n xs ys cumul-xs cumul-ys l-num :right :left))
         (maxf res (solve n xs ys cumul-xs cumul-ys l-num :right :right)))
    (println res)))

#-swank (main)

;;;
;;; Test and benchmark
;;;

#+swank
(defun io-equal (in-string out-string &key (function #'main) (test #'equal))
  "Passes IN-STRING to *STANDARD-INPUT*, executes FUNCTION, and returns true if
the string output to *STANDARD-OUTPUT* is equal to OUT-STRING."
  (labels ((ensure-last-lf (s)
             (if (eql (uiop:last-char s) #\Linefeed)
                 s
                 (uiop:strcat s uiop:+lf+))))
    (funcall test
             (ensure-last-lf out-string)
             (with-output-to-string (out)
               (let ((*standard-output* out))
                 (with-input-from-string (*standard-input* (ensure-last-lf in-string))
                   (funcall function)))))))

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    (run-program "powershell.exe" '("-Command" "Get-Clipboard") :output out :search t)))

#+swank (defparameter *this-pathname* (uiop:current-lisp-file-pathname))
#+swank (defparameter *dat-pathname* (uiop:merge-pathnames* "test.dat" *this-pathname*))

#+swank
(defun run (&optional thing (out *standard-output*))
  "THING := null | string | symbol | pathname

null: run #'MAIN using the text on clipboard as input.
string: run #'MAIN using the string as input.
symbol: alias of FIVEAM:RUN!.
pathname: run #'MAIN using the text file as input."
  (let ((*standard-output* out))
    (etypecase thing
      (null
       (with-input-from-string (*standard-input* (delete #\Return (get-clipbrd)))
         (main)))
      (string
       (with-input-from-string (*standard-input* (delete #\Return thing))
         (main)))
      (symbol (5am:run! thing))
      (pathname
       (with-open-file (*standard-input* thing)
         (main))))))

#+swank
(defun gen-dat ()
  (uiop:with-output-file (out *dat-pathname* :if-exists :supersede)
    (format out "")))

#+swank
(defun bench (&optional (out (make-broadcast-stream)))
  (time (run *dat-pathname* out)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "10 3
2
7
9
"
    "15
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "10 6
1
2
3
6
7
9
"
    "27
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "314159265 7
21662711
77271666
89022761
156626166
160332356
166902656
298992265
"
    "1204124749
")))


Measured memory_bytes: 39524