What is the lowest grid with time of +0.499,when laps are larger than 21?
CREATE TABLE "250cc_classification" (
  "rider" text,
  "manufacturer" text,
  "laps" real,
  "time" text,
  "grid" real
);
SELECT MIN("grid") FROM "250cc_classification" WHERE "time"='+0.499' AND "laps">21;