｜1/4-1/2｜+｜1/6-1/4｜+｜1/8—1/6｜+.+｜1/2008-1/2006｜
=1/2-1/4+1/4-1/6+1/6-1/8+...+1/2006-1/2008
=1/2-1/2008
=1003/2008