What is the total enrollment of the aa IHSAA class?
CREATE TABLE "indiana_high_school_athletics_conference" (
  "school" text,
  "location" text,
  "mascot" text,
  "enrollment" real,
  "ihsaa_class" text,
  "ihsaa_football_class" text,
  "num_county" text
);
SELECT COUNT("enrollment") FROM "indiana_high_school_athletics_conference" WHERE "ihsaa_class"='aa';