(let [in "68+249*201-87"
      pred (set "+*-/")]
  (second
   (last
    (take-while #(< (first %) 2)
                (reductions (fn [[count acc] item]
                              [(if (pred item)
                                 (inc count)
                                 count)
                               (conj acc item)])
                            [0 []]
                            in)))))
[\6 \8 \+ \2 \4 \9]