from how many different institutes have the members of admiral of the fleet graduated ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open var_x dbo_militaryRank dbr_Admiral_of_the_Fleet_ attr_open Royal_Navy attr_close sep_dot var_x dbo_almaMater var_uri sep_dot var_uri a dbo_EducationalInstitution brack_close