(asdf:load-system "cl-strings")

(require :cl-strings)

(defvar *input*
  (mapcar (lambda (line)
            (mapcar (lambda (column) (parse-integer column))
                    (cl-strings:split line " ")))
          (uiop:with-safe-io-syntax ()
            (uiop:read-file-lines "input.txt"))))

(defun gradual-diff-p (record)
  (cond
    ((null (cdr record)) t)
    ((not (< 0 (abs (- (car record) (cadr record))) 4)) nil)
    (t (gradual-diff-p (cdr record)))))

(defun safep (record)
  (and (or (apply #'< record)
           (apply #'> record))
       (gradual-diff-p record)))

(length (delete nil (mapcar #'safep *input*)))