(println
 (loop [lines (rest (line-seq (clojure.java.io/reader *in*)))
        numbers #{}]
   (if (empty? lines)
     (count numbers)
     (let [n (Long/parseLong (first lines))]
       (recur (rest lines)
              (if (contains? numbers n)
                (disj numbers n)
                (conj numbers n)))))))
