How to install the specific version of postgresql?

I need to install a postgresql 9.6.6 on Ubuntu 14.04, but the command

apt-get install postgresql-9.6

installes 9.6.7.

How can I install 9.6.6?

An output of command

apt-cache policy postgresql-9.6

is

 Installed: 9.6.7-1.pgdg14.04+1 Candidate: 9.6.7-1.pgdg14.04+1 Version table: *** 9.6.7-1.pgdg14.04+1 0 100 /var/lib/dpkg/statusPackages 100 /var/lib/dpkg/status

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