m-2m-3m+4m-5m-6m+7m.2004m
=(1-2-3+4-5-6+7-8-9+...2002-2003-2004)m
=(-4-7-10-..-2005)m
=-(4+7+10+..+2005)m
=-(4+2005)*668/2m
=-671006m