Reading package lists... Done
Building dependency tree
Reading state information... Done
mdm is already the newest version.
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 gnome-core : Depends: gdm (>= 3.0) but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).