(1 - 1/2)*(1 - 1/3)*...*(1 - 1/2009)*(1 - 1/2010)
=(1/2) * (2/3) *...* (2008/2009) * (2009/2010)
=(1*2*3*...*2009)/(2*3*...*2009*2010)
=1/2010