what is the lowest viewers (m) when the share is more than 13?
CREATE TABLE "weekly_ratings" (
  "episode" text,
  "air_date" text,
  "rating" real,
  "share" real,
  "18_49_rating_share" text,
  "viewers_m" real,
  "rank_timeslot" text
);
SELECT MIN("viewers_m") FROM "weekly_ratings" WHERE "share">13;