What country would you cross if you flew in a strait line from belgrade Yugoslavia to vienna austria?

First of all, you would have to travel through time, not just cross national boundaries, because Yugoslavia has not existed for over 20 years!

Next, I am not sure what a "strait" line is. There are no straits in the region. On the surface of a sphere (or spheroid) such as the earth, the shortest distance between two points is a arc of the great circle, not a straight line drawn on a map which is a 2-d projection of a 3-d surface.

A great arc flight would take you over Hungary.
First of all, you would have to travel through time, not just cross national boundaries, because Yugoslavia has not existed for over 20 years!

Next, I am not sure what a "strait" line is. There are no straits in the region. On the surface of a sphere (or spheroid) such as the earth, the shortest distance between two points is a arc of the great circle, not a straight line drawn on a map which is a 2-d projection of a 3-d surface.

A great arc flight would take you over Hungary.