Write SQL query to solve given problem: How many Federalist representatives are there whose first names are Benjamin?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T.bioguide_id) FROM ( SELECT T1.bioguide_id FROM historical AS T1 INNER JOIN `historical-terms` AS T2 ON T1.bioguide_id = T2.bioguide WHERE T1.first_name = 'Benjamin' AND T2.party = 'Federalist' AND T2.type = 'rep' GROUP BY T1.bioguide_id ) AS T