(define yuki791
  (let*
    (
      (ls (string->list (read-line)))
      (pred
        (or
          (< (length ls) 2)
          (char>? (car ls) #\1)
          (not (every (^x (char=? x #\3)) (cdr ls)))))
      (f (lambda (xs) (if pred -1 (length (cdr xs))))))
    (write (f ls))
    (newline)))