What is the production code number for episode named "chilly scenes of winter golf"?
CREATE TABLE "table1_18646432_4" (
  "series_num" text,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "prod_code" real
);
SELECT MIN("prod_code") FROM "table1_18646432_4" WHERE "title"='\"Chilly Scenes of Winter Golf\"';