Count the number of female students who belong to marines organization.
female students refers to enlist.name who are NOT in male.name; organization refers to organ; organ = 'marines';
SELECT COUNT(*) FROM person AS T1 INNER JOIN enlist AS T2 ON T1.name = T2.name LEFT JOIN male AS T3 ON T1.name = T3.name WHERE T2.organ = 'marines' AND T3.name IS NULL