what is the most episodes when the average ratings is 18.8%?
CREATE TABLE "2006_fall_season" (
  "japanese_title" text,
  "romaji_title" text,
  "tv_station" text,
  "episodes" real,
  "average_ratings" text
);
SELECT MAX("episodes") FROM "2006_fall_season" WHERE "average_ratings"='18.8%';