ORA-00059: maximum number of DB_FILES exceeded

SQL>  sho parameter db_files

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_files                             integer     200
SQL> alter system set db_files = 1000 scope = spfile;

System altered.

SQL>
SQL> shut immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.

Total System Global Area 1.9003E+10 bytes
Fixed Size                  2399752 bytes
Variable Size            2256536056 bytes
Database Buffers         1.6735E+10 bytes
Redo Buffers                9273344 bytes
Database mounted.
Database opened.
SQL> sho parameter db_files

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_files                             integer     1000