What is the grid number of Sandro Cortese, who has Aprilia as the manufacturer and less than 19 laps?
CREATE TABLE "125cc_classification" (
  "rider" text,
  "manufacturer" text,
  "laps" real,
  "time_retired" text,
  "grid" real
);
SELECT SUM("grid") FROM "125cc_classification" WHERE "manufacturer"='aprilia' AND "laps"<19 AND "rider"='sandro cortese';