(define (fib2 n) (let loop ((m 0) (k 1) (count n)) (if (= count 0) m (loop k (+ m k) (- count 1)))))
(define (fib n) (cond ((= n 0) 0) ((= n 1) 1) (else (+ (fib (- n 1)) (fib (- n 2))))))