What is the total number of episodes where hugh laurie was the 3rd performer?
CREATE TABLE "radio_series" (
  "date" text,
  "episode" real,
  "performer_1" text,
  "performer_2" text,
  "performer_3" text,
  "performer_4" text
);
SELECT COUNT("episode") FROM "radio_series" WHERE "performer_3"='hugh laurie';