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(define (recur-cycle n)
(define (div_2_5 x)
(cond
((= (remainder x 2) 0)
(div_2_5 (/ x 2)))
((= (remainder x 5) 0)
(div_2_5 (/ x 5)))
(else x)))
(define (try-iter m r)
(if (= r 1)
m
(try-iter (+ m 1) (remainder (* r 10) n))))
(if (= (div_2_5 n) n)
(if (= n 1)
0
(try-iter 1 (remainder 10 n)))
(recur-cycle (div_2_5 n))))
(define (longest upper)
(define (try-iter n ans anscycle)
(if (> n upper)
ans
(let ((m (recur-cycle n)))
(if (> m anscycle)
(try-iter (+ n 1) n m)
(try-iter (+ n 1) ans anscycle)))))
(try-iter 1 1 0))
(display (longest (read)))
(newline)
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