Table: race_results_2007_3
Columns: rider
manufacturer
laps
time_retired
grid

Question: What is the grid number of Sandro Cortese, who has Aprilia as the manufacturer and less than 19 laps?
SQL: SELECT SUM("grid") FROM race_results_2007_3 WHERE "manufacturer" = 'aprilia' AND "laps" < 19 AND "rider" = 'sandro cortese'