Find the id of users who are followed by Mary and Susan.
select t2.f1 from user_profiles as t1 join follows as t2 on t1.uid = t2.f2 where t1.name = "Mary" intersect select t2.f1 from user_profiles as t1 join follows as t2 on t1.uid = t2.f2 where t1.name = "Susan"