crystal, 116 bytes

Result

AC

Duration

1851ms

Code [DL]

Y=`dd`.split;i=2;_,_,_,a,b,c,d,e,f,g,h,i=Y.map{|e|i+=1;e.to_i-Y[i%3].to_i};p (a*e*i+b*f*g+c*d*h-a*h*f-b*i*d-c*g*e)/6

stdin

81 27 99
03 65 65
90 66 30
95 46 10

stdout

29160

stderr

0+1 records in
0+1 records out
36 bytes copied, 0.000101955 s, 353 kB/s

strace