How to automatically add user to "default" organic group during registration?

Hi,

Have a question about OG 7.2 and Rules

For example:

Have a community built on OG, and want that every new member of site to be automatically added to some specific group (like "Security and other important announcements") during registration.

Lets assume, that group "Security and other important announcements" is node/1

I cannot find in Rules interface how to do this. I should be simple, as there is event "User is validated" and action "Subscribe user to group" but still do not understand data selector.

Which one to choose?

Thank you in advance.

p.s. beginner Rules user, please be patient