Find the Default user present in Oracle 12c

SQL> set line 200 pages 200
SQL> col username for a40
SQL> select username from dba_users where ORACLE_MAINTAINED='Y';

USERNAME
----------------------------------------
SYS
SYSTEM
XS$NULL
LBACSYS
OUTLN
DBSNMP
APPQOSSYS
DBSFWUSER
GGSYS
ANONYMOUS
CTXSYS
SI_INFORMTN_SCHEMA
DVF
DVSYS
GSMADMIN_INTERNAL
ORDPLUGINS
MDSYS
OLAPSYS
ORDDATA
XDB
WMSYS
ORDSYS
GSMCATUSER
MDDATA
REMOTE_SCHEDULER_AGENT
SYSBACKUP
GSMUSER
SYSRAC
OJVMSYS
AUDSYS
DIP
SYSKM
ORACLE_OCM
SYS$UMF
SYSDG

35 rows selected.