How many gold medals does Henk Jan Zwolle have?
gold medals refer to medal_name = 'Gold';
SELECT COUNT(T1.id) FROM person AS T1 INNER JOIN games_competitor AS T2 ON T1.id = T2.person_id INNER JOIN competitor_event AS T3 ON T2.id = T3.competitor_id INNER JOIN medal AS T4 ON T3.medal_id = T4.id WHERE T1.full_name = 'Henk Jan Zwolle' AND T4.medal_name = 'Gold'