What is the highest crowd number of the game where the away team was south melbourne?
CREATE TABLE "round_3" (
  "home_team" text,
  "home_team_score" text,
  "away_team" text,
  "away_team_score" text,
  "venue" text,
  "crowd" real,
  "date" text
);
SELECT MAX("crowd") FROM "round_3" WHERE "away_team"='south melbourne';