What is the average number of floors at 170 Fourth Avenue North?
CREATE TABLE "timeline_of_tallest_buildings" (
  "name" text,
  "street_address" text,
  "years_as_tallest" text,
  "height_ft_m" text,
  "floors" real
);
SELECT AVG("floors") FROM "timeline_of_tallest_buildings" WHERE "street_address"='170 fourth avenue north';