the shortest path has length 18
the cities on the shortest path are:
  1 3 2 4 
RTS warning: blocked process: Worker.worker : file shared.mpd, line 50
RTS warning: blocked process: Worker.worker : file shared.mpd, line 50
RTS warning: blocked process: Worker.worker : file shared.mpd, line 50
RTS warning: blocked process: Worker.worker : file shared.mpd, line 50