(define v (map string->number (string-split (read-line) " ")))
(define (c i v)
  (cond ((= (length v) 1) (if (= (car i) (car v)) 10 9))
        ((= (car i) (car v)) (c (cdr i) (cdr v)))
        (else (car i))))
(print (c (iota 10 1) v))