(1/2004-1)*(1/2003-1)*……*(1/1000-1)
=(-1)^(2004-1000+1)*(2003/2004)*(2002/2003)*……*(999/1000)
=-1*(999/2004)
=-999/2004
=-333/668
(1/2004-1)*(1/2003-1)*……*(1/1000-1)
=(-1)^(2004-1000+1)*(2003/2004)*(2002/2003)*……*(999/1000)
=-1*(999/2004)
=-999/2004
=-333/668