Question: What is the difference in overall student enrollment and international student enrollment at the Harvard university from 2011 to 2012?
SQL: SELECT SUM(T1.num_students) - SUM(CAST(T1.num_students * T1.pct_international_students AS REAL) / 100) FROM university_year AS T1 INNER JOIN university AS T2 ON T1.university_id = T2.id WHERE T2.university_name = 'Harvard University' AND T1.year BETWEEN 2011 AND 2012