How many male clients in 'Hl.m. Praha' district?
District data appears in the A2; Male means that gender = 'M'
SELECT COUNT(T1.client_id) FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id WHERE T1.gender = 'M' AND T2.A2 = 'Hl.m. Praha'