#lang scheme
(provide handle)
(define (handle) (define in (read-line))
  (define (fib n)
    (define (fof n a b)
      (cond ((= n 0) a)
            ((= n 1) b)
            (#t (fof (- n 1) b (+ a b)))))
   (fof n 0 1))
 (define num (string->number in))
 (if (number? num) (displayln (fib num)) (error "Input not a number")))