Assume graphs are simple and undirected

We say a graph G is self-complementary if G is isomorphic to its complement G. Explain why no graph having only two or three vertices can be self-complementary without enumerating the isomorphisms of all such gruphs. Hint: Think about the number of edges that could exist in a graph having two or three vertices. Also think about what must be true about the number of edges in graphs that are isomorphic to each other