It used to be that way, but Ukr border control has instituted a '90 out of every 180 days' rule. You can get around that with a proper business visa (usually granted for 1 year), or by using two passports, or by paying a fine upon leaving the country if you overstay.
No worries at all - sooooo, I've never been fined myself but the stories I hear vary from expat to expat. One refused to pay and got a 'black stamp' in their passport barring them from reentry for 6+ months.