You use Sarrus rule, and perform the following multiplications of diagonal items:
diagonals from left to right (using wrap around)
+14*8*5
+-13*-1*-10
+0*3*-2
diagonals from right to left are subtracted
-0*8*-10
--13*3*5
-14*-1*-2
is 560-130+0 - 0+195-28 = 597