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

Calculating dependencies ...

!!! Problem resolving dependencies for =sys-apps/accountsservice-26.27.3
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=sys-apps/accountsservice-26.27.3" 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 )