Who did Cain marry if his parents were the first 2 people on earth?

Genesis 4:16

Then Cain went out from the presence of the LORD and dwelt in the land of Nod on the east of Eden. And Cain knew his wife, and she conceived and bore Enoch.

Who are these people in Nod? 

They are the children of Adam and Eve. Cain met family who previously moved there. Adam lived 930 years. Over the period of 930 years Eve was capable of giving birth to lots of children; who then had children, ect.