1 0 -1 2
-2 1 3 1
0 1 0 -1
1 3 4 -2
=
1 0 0 0
-2 1 1 5
0 1 0 -1
1 3 5 -4
=
1 1 5
1 0 -1
3 5 -4
=25-3+4+5=31