(defvar state)
(setq state 'zero )
;state
;zero
;f5
;sev
;s5

(defvar ans)
(setq ans "NG~%")
(loop for char = (read-char nil nil) do
        (if (eq char nil) (return))
        (if (not (eq char #\Newline)) (progn
                (values)
        ))
        (case state
                ('zero
                        ;(print "zero")
                        (if (eql char #\5) (setq state 'f5))
                )
                ('f5   ;(print "f5")
                        (if (eql char #\7) (setq state 'sev) (setq state 'zero))
                )
                ('sev  ;(print "sev")
                        (if (eql char #\5) (progn (setq ans "OK~%") (return)) (setq state 'zero))
                )
        )
)
(format 't ans)