m-2m-3m+4m-5m-6m=

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
等差数列公式：
Sn=n(a1+an)/2
an=a1+(n-1)d