What's the least amount of floors at 921 sw sixth avenue?
CREATE TABLE "timeline_of_tallest_buildings" (
  "name" text,
  "street_address" text,
  "years_as_tallest" text,
  "height_feet_m" text,
  "floors" real
);
SELECT MIN("floors") FROM "timeline_of_tallest_buildings" WHERE "street_address"='921 sw sixth avenue';