What is the highest week that had a game against the Pittsburgh Steelers with 22,597 fans in attendance?
CREATE TABLE "schedule" (
  "week" real,
  "date" text,
  "opponent" text,
  "result" text,
  "attendance" real
);
SELECT MAX("week") FROM "schedule" WHERE "attendance"<'22,597' AND "opponent"='pittsburgh steelers';