What is the highest episode number written by Harry Winkler?
CREATE TABLE "table1_2342078_4" (
  "episode_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_airdate" text,
  "production_code_num" real
);
SELECT MAX("episode_num") FROM "table1_2342078_4" WHERE "written_by"='Harry Winkler';