With problems like these, the best thing to do is to draw a diagram. In this problem you have a straight path, but it is broken into segments.
So now you have an array of segments: each jogger has their own array of segments and we assume that they only run on one local track each (i.e. the jogger runs on say segment 2-4 but they don't go on say 2-3 then skip 4 and then run on segment 5).
So basically you have a min and max value for the segments that a particular jogger runs and now you have to identify the actual segments that need a billboard.
So for your data structure is an array of pairs: each item corresponds to a joggers start and end segment. You have to use that info to detect which segments need a billboard.
I'll ask you to attempt to write some pseudo-code that includes the conditions for going through the pairs and then checking what segments are required for a billboard for that given pair.