Isn't it about languages, not countries?
When it's about languages, you count language users.
When it's about languages, you count language users.
So we then we should count ukrainians and belorussians separately.
If we're counting this by language, we should figure out how much Ukrainians (or Belorusians) use internet in russian language, primary, and how much don't; and then we should sum up those numbers. Everything else would be a speculation.