How many episodes are there for the three darts challenge with Sharon Osbourne?
CREATE TABLE "table1_26733129_1" (
  "episode_number" real,
  "air_date" text,
  "guests" text,
  "three_darts_challenge" text,
  "musical_performance" text
);
SELECT MAX("episode_number") FROM "table1_26733129_1" WHERE "three_darts_challenge"='Sharon Osbourne';