ssh login failed

[root@ajeesh ~]# ssh root@192.16.15.18
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
a3:d6:34:8d:81:74:aj:ee:sh:B:ka:nn:an:2a:2d:95.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending key in /root/.ssh/known_hosts:18
RSA host key for 192.16.15.18 has changed and you have requested strict checking.
Host key verification failed.

Solution:
[root@ajeesh ~]# ssh-keygen -R 192.16.15.18
/root/.ssh/known_hosts updated.
Original contents retained as /root/.ssh/known_hosts.old

suppose you are trying to connect to the server using hostname
Solution:-
[root@ajeesh ~]# ssh-keygen -R server1.ajeesh.com