Question: Among the institutes in the state of Alabama whose percent rank for median SAT value within sector is 77, how many of them have over 500 graduates in total in 2011?
SQL: SELECT COUNT(DISTINCT T1.chronname) FROM institution_details AS T1 INNER JOIN institution_grads AS T2 ON T2.unitid = T1.unitid WHERE T1.state = 'Alabama' AND T1.med_sat_percentile = '100' AND T2.year = 2011 AND T2.grad_cohort > 500