Table: australian_football_night_series
Columns: season
premier
runner_up
score
venue
attendance
premiership

Question: If the season is before 2000, the runner up was north melbourne, and it's the pre-season cup, what's the sum of attendees?
SQL: SELECT SUM("attendance") FROM australian_football_night_series WHERE "premiership" = 'pre-season cup' AND "runner_up" = 'north melbourne' AND "season" < 2000