These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.93 s (backtrack: 0/20).


The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by gnome-extra/cinnamon-screensaver-6.6.1::gentoo
# required by =gnome-extra/cinnamon-screensaver-6.6.1 (argument)
>=x11-libs/gtk+-3.24.52 introspection

!!! The ebuild selected to satisfy "sys-apps/accountsservice" has unmet requirements.
- sys-apps/accountsservice-26.27.3::gentoo USE="-doc -elogind -gtk-doc -introspection (-selinux) (-systemd) -test -vala -xcrypt"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( elogind systemd )

(dependency required by "gnome-extra/cinnamon-screensaver-6.6.1::gentoo" [ebuild])
(dependency required by "=gnome-extra/cinnamon-screensaver-6.6.1" [argument])