CREATE TABLE table_204_455 (id DECIMAL, "rd." DECIMAL, "grand prix" TEXT, "date" TEXT, "location" TEXT, "pole position" TEXT, "fastest lap" TEXT, "winning driver" TEXT, "constructor" TEXT, "report" TEXT)

how many races occurred before alain prost won a pole position ?
SELECT COUNT(*) FROM table_204_455 WHERE "rd." < (SELECT "rd." FROM table_204_455 WHERE "pole position" = 'alain prost' ORDER BY "rd." LIMIT 1)
SELECT COUNT(*) FROM "table_204_455" WHERE "rd." < (SELECT "rd." FROM "table_204_455" WHERE "pole position" = 'alain prost' ORDER BY "rd." NULLS FIRST LIMIT 1)