How many students are enlisted in the Peace Corps organization are enrolled in UCSD school?
enlisted in the Peace Corps refers to organ = 'peace_corps'; enrolled in UCSD school refers to school = 'ucsd';
SELECT COUNT(T1.name) FROM enlist AS T1 INNER JOIN enrolled AS T2 ON T1.name = T2.name WHERE T1.organ = 'peace_corps' AND T2.school = 'ucsd'