How do I do (apt-get -f install)?

ts1-deb:~# apt-get install ntp
Reading package lists... Done
Building dependency tree
Reading state information... Done
ntp is already the newest version.
You might want to run `apt-get -f install' to correct these:
The following packages have unmet dependencies:
dovecot-imapd: Depends: dovecot-common (= 1:1.0.15-2.3+lenny1) but it is not going to be installed
dovecot-pop3d: Depends: dovecot-common (= 1:1.0.15-2.3+lenny1) but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
ts1-deb:~#

ts1-deb:~# apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following extra packages will be installed:
dovecot-common
The following NEW packages will be installed:
dovecot-common
0 upgraded, 1 newly installed, 0 to remove and 23 not upgraded.
2 not fully installed or removed.
Need to get 0B/2106kB of archives.
After this operation, 4923kB of additional disk space will be used.
Do you want to continue [Y/n]? y
(Reading database ... 26483 files and directories currently installed.)
Unpacking dovecot-common (from .../dovecot-common_1%3a1.0.15-2.3+lenny1_amd64.deb) ...
mv: `/etc/dovecot.conf' and `/etc/dovecot/dovecot.conf' are the same file
dpkg: error processing /var/cache/apt/archives/dovecot-common_1%3a1.0.15-2.3+lenny1_amd64.deb (--unpack):
subprocess pre-installation script returned error exit status 1
Errors were encountered while processing:
/var/cache/apt/archives/dovecot-common_1%3a1.0.15-2.3+lenny1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
ts1-deb:~#