Which Round has the Winning Driver of brendon hartley, and a Date of 27 april?
CREATE TABLE "calendar" (
  "round" real,
  "circuit" text,
  "date" text,
  "pole_position" text,
  "fastest_lap" text,
  "winning_driver" text,
  "winning_team" text
);
SELECT MIN("round") FROM "calendar" WHERE "winning_driver"='brendon hartley' AND "date"='27 april';