aptitude:Logical Reasoning :: Number Series

I will be   DAILY POSTING A APTITUDE QUESTION IN DIFFRENT STREAMS AND IF U CAN SOLVE THAT ,U  CAN ANSWER THE QUESTION AS YOUR COMMENT..,IF NOT THE NEXT DAY I'LL ANSWER THE QUESTION AS A COMMENT ..SO THAT U CAN IMPROVE YOUR APTITUDE SKILL..:)

Look at this series: 2, 1, (1/2), (1/4), ... What number should come next?