How to find a list of regions that are no more than X km away. from given?

Question

Cartography

The task is trivial.
There is a list of regions of the Russian Federation where the company's plants are located.
It is required to set geotargeting in Yandex.Direct for all regions that are no more than 350 km away. from any of the given cities (that is, roughly speaking, to neighboring regions). Yes, you can look at the map, but suddenly there is such a service.