How many cities are there in the country ruled by Kostis Stefanopoulos?
ruled by Kostis Stefanopoulos refers to HeadOfState = 'Kostis Stefanopoulos';
SELECT COUNT(DISTINCT T1.Name) FROM City AS T1 INNER JOIN Country AS T2 ON T1.CountryCode = T2.Code WHERE T2.HeadOfState = 'Kostis Stefanopoulos'