SCHEMA:
CREATE TABLE table_name_5 (laps INTEGER, bike VARCHAR, grid VARCHAR, time VARCHAR)
USER:
What is the sum of the laps with a grid less than 28, retirement time, and a ducati 1098 f08 bikes?

QUERY:
SELECT SUM(laps) FROM table_name_5 WHERE grid < 28 AND time = "retirement" AND bike = "ducati 1098 f08"