How could Cain get married?

In the bible, it clearly says that after Cain kills his brother Abel, he goes and takes himself a wife in another country. But if Eve by this time only had given birth to Cain and Abel, where did the wife come from? I know that Adam and Eve had more kids than Cain, Abel and Seth, but did they really have enough for it to be more than one country? I personally find this whole thing pretty f*cked up, so I would be pretty thankful if anyone could explain it to me