According to OSM I would need 8 days and 23 h !!
Countries crossed : Switzerland, Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Romania
The stages, basically ... as they were used to determine this route.
Negotin, Negotin, Serbia
Podul Prieteniei Giurgiu-Ruse, Romania
The contour lines, very indicative (there is normally not the second very short peak at 500m)