[ a  0  0 -h  0 -l]
[-b  0  0  0  j  l]
[ 0  c  0 -g -j  0]
[ 0 -d  0  g  0  k]
[ 0  0  e  0 -i -k]
[ 0  0 -f  h  i  0]

a*c*e + b*d*f