how to install kdm on CentOS 7

I installed CentOS 7, first i installed group "KDE Plasma Workspace", then I installed "GNOME Desktop", after that, I found only 'gdm' existed. and 'which kdm' eturns nothing, 'yum provides kdm' only returns 'kgreeter-xxx' but it has been installed.

my question is whether the kdm removed from CentOS 7. how can install kdm on CentOS 7.

Thanks!