Find the cities

Rahul had recently won a prestigious prize, He was thus being called from n cities for giving lectures. The cities were connected (if at all) only by unidirectional roads.But Rahul was a miser. He would only prefer to travel by road as its the cheapest. Thus, he will go to a certain city by road, if and only if he can return by some road too. Now Rahul needs your help. If he is present in a certa