Ubuntu 14.04 LTS install problem

I installed Ubuntu 14.04 LTS
apg-get update ... apt-get upgrade ...

and looked at
www.postgresql.org/download/linux/ubuntu
then added apt repository /etc/apt/sources.list.d/pgdg.list

When I try

apt-get install postgresql-9.4

error:
.... depends on postgresql-common (>= 142~) what should not get installed
... you have defect packages ...

any ideas?

Urs