Calculation: 1 + 2-3-4 + 5 + 6-7-8 + 9 + 10-11-12 + +2005+2006-2007-2008.

Calculation: 1 + 2-3-4 + 5 + 6-7-8 + 9 + 10-11-12 + +2005+2006-2007-2008.

The original formula = (1 + 2-3-4) + (5 + 6-7-8) + (9 + 10-11-12) + +(2005+2006-2007-2008)=(-4)+(-4)+(-4)+… +(-4)=(-4)×502=-2008.