Problem with deleting observations

Hi all,

I would like to ask you how I can deal with below situation.
When two CEOs are observed in the same year of the same firm, I want to delete an observation which has the smaller size of "becomeCEO".
For example, I want to delete observation of CEOid 100 and 200 in the following example, since they have the smaller size of "becomeCEO" comparing to that of CEOid 101 and 201, respectively;

firmid....CEOid.......year.......becomeCEO
1001.....100...........1994......1990
1001.....101...........1994......1994
...
1003.....200...........2000......1998
1003.....201...........2000......2000

I appreciate your codes and help in advance!

Regards,