What is the highest pick number of a defensive back with less than 136 overall points?
CREATE TABLE "atlanta_falcons_draft_history" (
  "round" real,
  "pick_num" real,
  "overall" real,
  "name" text,
  "position" text,
  "college" text
);
SELECT MAX("pick_num") FROM "atlanta_falcons_draft_history" WHERE "overall"<136 AND "position"='defensive back';