Related dropdown lists

Hello! I really need help!  I need to implement two dropdown lists. The first one, for example, contains REGIONS, and the second one contains CITIES. The second list is inactive until a REGION is selected in the first one. Accordingly, when a REGION is selected, the second list becomes active and contains the CITIES of the selected REGION.

Hierarchical Select is not suitable because it creates a second field after a selection is made in the first one.

I have been struggling with this seemingly simple task for three days now. A Google search did not yield any results. 

I kindly ask for help or at least some guidance in the right direction.