Problem:
Score : 500 points

Problem Statement

We have a sequence of N integers: A_1, A_2, \cdots, A_N.

You can perform the following operation between 0 and K times (inclusive):

Choose two integers i and j such that i \neq j, each between 1 and N (inclusive). Add 1 to A_i and -1 to A_j, possibly producing a negative element.

Compute the maximum possible positive integer that divides every element of A after the operations. Here a positive integer x divides an integer y if and only if there exists an integer z such that y = xz.

Constraints

2 \leq N \leq 500

1 \leq A_i \leq 10^6

0 \leq K \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K
A_1 A_2 \cdots A_{N-1} A_{N}

Output

Print the maximum possible positive integer that divides every element of A after the operations.

Sample Input 1

2 3
8 20

Sample Output 1

7

7 will divide every element of A if, for example, we perform the following operation:

Choose i = 2, j = 1. A becomes (7, 21).

We cannot reach the situation where 8 or greater integer divides every element of A.

Sample Input 2

2 10
3 5

Sample Output 2

8

Consider performing the following five operations:

Choose i = 2, j = 1. A becomes (2, 6).

Choose i = 2, j = 1. A becomes (1, 7).

Choose i = 2, j = 1. A becomes (0, 8).

Choose i = 2, j = 1. A becomes (-1, 9).

Choose i = 1, j = 2. A becomes (0, 8).

Then, 0 = 8 \times 0 and 8 = 8 \times 1, so 8 divides every element of A. We cannot reach the situation where 9 or greater integer divides every element of A.

Sample Input 3

4 5
10 1 2 22

Sample Output 3

7

Sample Input 4

8 7
1 7 5 6 8 2 6 5

Sample Output 4

5

Solution in Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

;; -*- coding: utf-8 -*-
(eval-when (:compile-toplevel :load-toplevel :execute)
  (defparameter OPT
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0)))
  #+swank (ql:quickload '(:cl-debug-print :fiveam))
  #-swank (set-dispatch-macro-character #\# #\> (lambda (s c p) (declare (ignore c p)) (read s nil (values) t))))
#+swank (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)
#-swank (disable-debugger) ; for CS Academy

;; BEGIN_INSERTED_CONTENTS
(declaim (ftype (function * (values (vector (integer 0 #.most-positive-fixnum)) &optional))
                enum-divisors))
(defun enum-divisors (x)
  "Enumerates all the divisors of X in O(sqrt(X)). Note that the resultant
vector is NOT sorted."
  (declare (optimize (speed 3))
           ((integer 0 #.most-positive-fixnum) x))
  (let* ((sqrt (isqrt x))
         (res (make-array (isqrt sqrt) ; FIXME: sets the initial size to x^1/4
                          :element-type '(integer 0 #.most-positive-fixnum)
                          :fill-pointer 0)))
    (loop for i from 1 to sqrt
          do (multiple-value-bind (quot rem) (floor x i)
               (when (zerop rem)
                 (vector-push-extend i res)
                 (unless (= i quot)
                   (vector-push-extend quot res)))))
    res))


(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  (declare #.OPT)
  (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

(defun calc-distance (div sum as)
  (declare ((simple-array uint32 (*)) as)
           (uint32 div sum)
           (inline sort))
  (let ((as (copy-seq as))
        (n (length as))
        (cumuls1 (make-array 501 :element-type 'uint62 :initial-element 0))
        (cumuls2 (make-array 501 :element-type 'uint62 :initial-element 0)))
    (declare (dynamic-extent cumuls1 cumuls2))
    (setf as (sort as (lambda (x y) (< (mod x div) (mod y div)))))
    (dotimes (i n)
      (setf (aref cumuls1 (+ i 1))
            (+ (aref cumuls1 i) (* div (floor (aref as i) div)))))
    (loop for i from (- n 1) downto 0
          do (setf (aref cumuls2 i)
                   (+ (aref cumuls2 (+ i 1)) (* div (ceiling (aref as i) div)))))
    (loop for i to n
          when (= sum (+ (aref cumuls1 i) (aref cumuls2 i)))
          do (return (- (reduce #'+ as :end i) (aref cumuls1 i)))
          finally (error "Huh?"))))

(defun main ()
  (let* ((n (read))
         (k (read))
         (as (make-array n :element-type 'uint32))
         (sum 0))
    (dotimes (i n)
      (setf (aref as i) (read-fixnum))
      (incf sum (aref as i)))
    (let ((divs (enum-divisors sum)))
      (setf divs (sort divs #'>))
      (loop for d across divs
            when (<= (calc-distance d sum as) k)
            do (println d)
               (return-from main)))))

#-swank (main)