Give the number of female users of "E派" brand devices.
female refers to gender = 'F'; E派 brand refers to phone_brand = 'E派';
SELECT COUNT(T2.device_id) FROM gender_age AS T1 INNER JOIN phone_brand_device_model2 AS T2 ON T1.device_id = T2.device_id WHERE T1.gender = 'F' AND T2.phone_brand = 'E派'