What is the smallest average for Beijing Guo'an when they played more than 240 games?
CREATE TABLE "season_averages" (
  "season" real,
  "total_attendance" real,
  "games" real,
  "average" real,
  "high_avg" real,
  "team" text,
  "no_of_clubs" real
);
SELECT MIN("average") FROM "season_averages" WHERE "team"='beijing guo''an' AND "games">240;