What is the average rank of the airport in São Paulo with passengers totaling less than 18,795,596?
CREATE TABLE "brazil_s_15_busiest_airports_by_passenge" (
  "rank" real,
  "location" text,
  "total_passengers" real,
  "annual_change" text,
  "capacity_in_use" text
);
SELECT AVG("rank") FROM "brazil_s_15_busiest_airports_by_passenge" WHERE "location"='são paulo' AND "total_passengers"<'18,795,596';