SELECT COUNT(*) FROM table_204_671 WHERE "number of episodes" >= 20
how many movies have at least 20 episodes ?
CREATE TABLE table_204_671 (
    id number,
    "airing\ndate" text,
    "english title\n(chinese title)" text,
    "number of episodes" number,
    "main cast" text,
    "theme song (t)\nsub-theme song (st)" text,
    "genre" text,
    "notes" text,
    "official website" text
)