CREATE TABLE table_204_641 (id DECIMAL, "pos" TEXT, "no" DECIMAL, "driver" TEXT, "constructor" TEXT, "laps" DECIMAL, "time/retired" TEXT, "grid" DECIMAL, "points" DECIMAL)

what is the number of drivers who did n't finish the race due to engine trouble ?
SELECT COUNT("driver") FROM table_204_641 WHERE "time/retired" = 'engine'
SELECT COUNT("driver") FROM "table_204_641" WHERE "time/retired" = 'engine'