I had to think twice which other countries also speak a Slavic language - I was basically guessing Uzbekistan, Turkmenistan, Tajikistan, Kyrgyzstan, Georgia, Armenia, Azerbaijan, Estonia, Lithuania, and Latvia. Actually, I was expecting to find Hungary perhaps, or Moldova and Romania.
Moldova is there, Romania and Hungary both have some Slavic minorities too, however not that significant. The countries of the former USSR, on the other hand, are full of Russians.