Country borders


I would like to set up a reverse geocoding service which returns the countrycode for a given lat/long-point. Therefore I would need to know the border lines of the European countries (to form a polygon). As I’m new to OSM, I don’t know if there is a possibility to get these borders and if so, how this can be done.
I would really appreciate any help.

Thanks in advance,

You might have luck with depending on how they’re tagged.