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(use-modules (srfi srfi-1)
(srfi srfi-42))
(define big-ass-number
"7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450")
(define (digit str i)
(string->number (substring str i (1+ i))))
(define (five-digits numstring start)
(list (digit numstring start)
(digit numstring (+ start 1))
(digit numstring (+ start 2))
(digit numstring (+ start 3))
(digit numstring (+ start 4))))
(define (five-digit-products numstring)
(list-ec (: i (- (string-length numstring) 6))
(apply * (five-digits numstring i))))
(reduce max 0 (five-digit-products big-ass-number))
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