Most likely Montenegro -> Serbia. Much easier, then going through two other countries, and Montenegro has issues (both election, and previous corruption problems).

Last time I passed through Montenegro I got stoped by two cops and they straight out asked me money (they wanted 20 euros for each), so they didn't suspend my license. (and yes, they were slavic/montenegrins and not Albanians)

I was going 64 khm/h on a 60km/h zone. They are corrupt as hell.