(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (dp (make-array 20001 :element-type 'integer :initial-element -123))
         (sieve (make-array 20001 :initial-element nil)))
    (setf (aref dp 0) 0)
    (loop for i from 2 to 20000 do
          (loop for j from (* i i) to 20000 by i do
                (setf (aref sieve j) t))
          (unless (aref sieve i)
                  (loop for j from (- 20000 i) downto 0 do
                        (setf (aref dp (+ i j)) (max (1+ (aref dp j)) (aref dp (+ i j)))))))
    (format t "~d~%" (max -1 (aref dp n)))))

(main)