(let ((lowest (apply #'min data))
        (highest (apply #'max data)))
    (loop for x from lowest to highest
          minimizing (fuel-cost data x #'compounding-cost))))

  (let* ((sum (reduce #'+ data))
         (count (length data)))
    (min (fuel-cost data (floor sum count) #'compounding-cost)
         (fuel-cost data (ceiling sum count) #'compounding-cost))))