How to drop an user?

 SQL> drop user 8900308 cascade;

drop user 8900908 cascade   
*ERROR at line 1:
ORA-01935: missing user or role name

SQL> !oerr ora 1935

01935, 00000, "missing user or role name"
// *Cause:  A user or role name was expected.
// *Action: Specify a user or role name.

SQL> drop user "8900908" cascade;

User dropped.

Normal user :

Syntax:

Drop user <username> cascade;