CREATE TABLE table_15785 ("Year" FLOAT, "Team" TEXT, "Co-Drivers" TEXT, "Class" TEXT, "Laps" FLOAT, "Pos." TEXT, "Class Pos." TEXT)

Name the sum of Laps for co-drivers of oliver gavin jan magnussen and class of gts with year less than 2004
SELECT SUM("Laps") FROM table_15785 WHERE "Co-Drivers" = 'oliver gavin jan magnussen' AND "Class" = 'gts' AND "Year" < '2004'
SELECT SUM("Laps") FROM "table_15785" WHERE "Class" = 'gts' AND "Co-Drivers" = 'oliver gavin jan magnussen' AND "Year" < '2004'