Holy Cow! A Brand New Feature

We just keep getting more and more fortunate. Mr. Haney, the Director of Operations Engineering for Lockheed Martin, has sent in some wonderful math problems for you to solve. Let's see who can come up with an answer first! Remember to explain how you arrived at your answer.

A farmer brings his cows to market for sale.
The 1st buyer buys half of the farmers cows, plus 1/2 a cow.
A 2nd buyer buys half of the remaining (after the 1st buyer) cows, plus 1/2 a cow.
The 3rd and final buyer buys half of the remaining (after the 1st and 2nd buyers) cows, plus 1/2 a cow.
All three buyers bought whole cows.
The farmer sold all of his cows he brought to market.

How many cows did the farmer bring to market?