1 month in eastern europe

hi everyone, i have a huge problem: too many interesting places to see in such a short time, so i need some help

march 1st: i arrive to prague
april 2nd: i have a ticket from athens to cairo,
april 5th: ticket Cairo - Madrid

as you can see i have 1 month to travel through eastern europe, i guess the best itinerary is:
prague 4 days
krakov 3
budapest 4
dubrovnik 2
zagreb 2
serbia&montengro 3
istanbul 4
greek islands 2
athens 2

26 days, missing many places, what do you think?? any opinions??

thanks!!!