ruby, 83 bytes

Result

AC

Duration

532ms

Code [DL]

require'matrix'
x=$<.map{|l|Vector[*l.split.map(&:to_i),1]}
p -Matrix.rows(x).det/6

stdin

04 94 61
59 20 50
87 35 05
98 41 26

stdout

18714

stderr

strace