(define (fib n)
  (if (< n 2) 1
      (+ (fib (- n 1)) (fib (- n 2)))))

(define (counting-fib n)
  (let ((counter (vector 0)))
    (let kernel ((n n))
      (vector-set! counter 0 (+ 1 (vector-ref counter 0)))
      (if (< n 2) 1
          (+ (kernel (- n 1)) (kernel (- n 2)))))
    (vector-ref counter 0)))