(import
  (scheme base)
  (scheme read)
  (scheme write)
  (gauche base)
  (gauche uvector)
)

(define yuki791
  (let*
    (
      (s (read-uvector <u8vector> 101))
      (len (uvector-length s))
      (ushi (make-u8vector len 51))
    )
    (uvector-set! ushi 0 49)
    (uvector-set! ushi (- len 1) 10)
    (cond
      ((not (equal? s ushi))
        (display "-1\n")
      )
      ((= len 2)
        (display "-1\n")
      )
      (else
        (write (- len 2))
        (newline)
      )
    )
  )
)