"CIS" (https://en.wikipedia.org/wiki/Commonwealth_of_Independent_St...) does not equal "Former USSR". Ukraine is not (and has neven been) a member of CIS. If you want to say "former USSR", just say "former USSR". Don't try to use "CIS" as a kind of a euphemism for "former USSR", this is simply a different thing with a different meaning.

Sorry for the rant, but I think someone will find it useful.