Calculate days between 2 dates

I need formula that calculates me amount of days from a certain date from the beginning of that year.
So for example 13/08/2009 has 217 days from 01/01/2009. The date 15/05/2010 has 135 days from 01/01/2010. So the question is how can I make formula that automatically recognize that I am in year 2010, 2009, 2011, etc

You could use the DATEDIF function.