user create in oracle 12c container

Hi friend I am using oracle 12c release 2. without accessing any pluggable database , just from containing I am trying to create a user. It is raising errors.

INSTANCE_NAME    STATUS

---------------- ------------

cdb1             OPEN

SQL> show user

USER is "SYS"

SQL> create user u1 identified by u1;

create user u1 identified by u1

            *

ERROR at line 1:

ORA-65096: invalid common user or role name

Regards

Jewel