(defn required-fuel [mass]
  (- (int (Math/floor (/ mass 3))) 2))

(with-open [r (clojure.java.io/reader "/tmp/input")]
  (->> (line-seq r)
       (filter not-empty)
       (map #(Integer/valueOf %))
       (map required-fuel)
       (reduce + 0))) ;; => 3452245