(def t1 (System/currentTimeMillis))
(def fib
  (memoize (fn [n]
             (if (<= n 1) 1
                 (+ (fib (- n 1))
                    (fib (- n 2)))))))
  (println (fib 42))
(def t2 (System/currentTimeMillis))
(println (- t2 t1))