ORA-01624: log %s needed for crash recovery of instance %s (thread %s)

SQL> alter database drop logfile group 3;
alter database drop logfile group 3
*
ERROR at line 1:
ORA-01624: log 3 needed for crash recovery of instance migdb (thread 1)
ORA-00312: online log 3 thread 1: 'D:\APP\INAM\ORADATA\MIGDB\REDO03.LOG'

Error:      ORA-01624  (ORA-1624)
Text:      log %s needed for crash recovery of instance %s (thread %s)
---------------------------------------------------------------------------
Cause:    A log cannot be dropped or cleared until the thread's checkpoint
    has advanced out of the log.
Action:    If the database is not open, then open it. Crash recovery will
    advance the checkpoint. If the database is open force a global
    checkpoint. If the log is corrupted so that the database cannot be
    opened, it may be necessary to do incomplete recovery until cancel
    at this log.

SQL> shutdown immediate
ORA-01507: database not mounted


ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1068937216 bytes
Fixed Size                  2262048 bytes
Variable Size             624954336 bytes
Database Buffers          436207616 bytes
Redo Buffers                5513216 bytes
Database mounted.
Database opened.

SQL> alter database drop logfile group 3;

Database altered.