How many males from Belgium have participated in an Olympic Games?
males refer to gender = 'M'; Belgium refers to region_name = 'Belgium';
SELECT COUNT(T2.person_id) FROM noc_region AS T1 INNER JOIN person_region AS T2 ON T1.id = T2.region_id INNER JOIN person AS T3 ON T2.person_id = T3.id WHERE T1.region_name = 'Belgium' AND T3.gender = 'M'