You can get to Sumy from Moscow by direct train, the train departs Moscow (Kievsky Train Station) daily at 5:23pm and arrives to Sumy next day at 6am. Alternatively, you can fly from Moscow to Kiev or Kharkiv and after that take a train, bus or mini-bus to Sumy.

How to get to Sumy from Kiev Boryspil Airport, Kiev or Kharkiv