1+2+3-4+5+6+7-8+.+85+86+87-88
=1+2+3+4+5+6+7+8+...+85+86+87+88-4*2-8*2-12*2-...-88*2
=(1+88)*88/2-8*1-8*2-8*3-...-8*22
=44*89-8*(1+2+3+...+22)
=44*89-8*(1+22)*22/2
=44*89-8*11*23
=44*89-44*46
=44*(89-46)
=44*43
=1892.