max -1x1 + 1x2 -4x4 +2x5 -2x6 -2x7 -2x8   
st 
 -1x1 +1x3 1x5 =  -3
      1x1-1x2+ 1x4 =  1
      1x2 -1x3 +1x6 -1x7 =  4 
      -1x4 -1x6+ 1x8 =  3
      -1x5 + 1x7 -1x8 = -5
end