m-2m-3m+4m-5m-6m= m-2m-3m+4m-5m-6m+···+2002m-2003m-2004m

m-2m-3m+4m-5m-6m+···+2002m-2003m-2004m
= [（1-2-3）+（4-5-6）+···（2002-2003-2004）]m
= -（4+7+11+···+2005）m
= -668*（4+2005）m/2
= -671006m
等差數列公式：
Sn=n（a1+an）/2
an=a1+（n-1）d