What is the lowest episode # with an air date of October 31, 2001?
CREATE TABLE "season_4_2001_2002" (
  "episode_num" real,
  "num_in_season" real,
  "episode_name" text,
  "airdate" text,
  "location" text
);
SELECT MIN("episode_num") FROM "season_4_2001_2002" WHERE "airdate"='october 31, 2001';