Euler problem 25

<pre lang="scheme">
;What is the first term in the
;Fibonacci sequence to contain 1000 digits?
(define (square x) (* x x))

(define (pow man exp)
  (cond
    ((= exp 0) 1)
    ((< exp 0) (/ 1 (pow exp (- man))))
    ((even? exp) (square (pow man (/ exp 2))))
    ((odd? exp) (* man (square (pow man (/ (- exp 1) 2)))))
    (else #f)))

(define (prob25 digits)
  (let ((big-const (pow 10 (- digits 1))))
    (let fib ((first 1) (second 1) (count 1))
      (if (>= first big-const)
          count
          (begin
            ;(display first) (display " ") (display count) (newline)
            (fib second (+ first second) (+ count 1))
            )))
    )
  )

(prob25 1000)</pre>