2006×(1-1/2)×(1-1/3)×(1-1/4)×(1-1/5)×……×(1-1/2005)×(1-1/2006)
=2006×1/2×2/3×3/4×4/5×……×2004/2005×2005/2006
=2006×1/2006
=1