2 - 4 - 6 + 8 + 10 - 12 - 14 + 16 + ...+ 2010 - 2012
= (2 - 4 - 6 + 8) + (10 - 12 - 14 + 16) + ...+ (2002 - 2004 - 2006 + 2008) + 2010 - 2012
= 0×251 - 2
= -2