(define (System.out.println x)
  (begin
    (write x)
    (newline)
  )
)

(let (
      (SoyBeans (* (read) (read)))
      (F (read))
     )
  (let loop(
            (RemainingBeans SoyBeans)
            (foo (read))
           )
    (if (eof-object? foo)
        (System.out.println RemainingBeans)
        (if (> 0 (- RemainingBeans foo))
            (System.out.println -1)
            (loop (- RemainingBeans foo) (read))
        )
    )
  )
)