How to determine the required archivelog files needed for a guaranteed restore point before running flashback database

SELECT DISTINCT al.thread#, al.sequence#, al.resetlogs_change#, al.resetlogs_time
FROM v$archived_log al,
     (select grsp.rspfscn               from_scn,
             grsp.rspscn                to_scn,
             dbinc.resetlogs_change#    resetlogs_change#,
             dbinc.resetlogs_time       resetlogs_time
        from x$kccrsp grsp,  v$database_incarnation dbinc
       where grsp.rspincarn = dbinc.incarnation#
         and bitand(grsp.rspflags, 2) != 0
         and bitand(grsp.rspflags, 1) = 1 -- guaranteed
         and grsp.rspfscn <= grsp.rspscn -- filter clean grp
         and grsp.rspfscn != 0
     ) grsp
  WHERE al.next_change#   >= grsp.from_scn
      AND al.first_change#    <= (grsp.to_scn + 1)
      AND al.resetlogs_change# = grsp.resetlogs_change#
      AND al.resetlogs_time       = grsp.resetlogs_time
      AND al.archived = 'YES';