The competition rules say:
You are not eligible to receive any Prize in the Competition if you are a resident of a country designated by the United States Treasury's Office of Foreign Assets Control.
Could you please list these designated countries or clarify what list you are referring to?
I tried to find out it myself but failed:
US Treasury’s Office website does not list such countries.
The Office of Foreign Assets Control (OFAC) does not maintain a specific list of countries that U.S. persons cannot do business with.
It also looks like Specially Designated Nationals list does not list countries, only persons, entities, vessels and aircrafts.