rust, 303 bytes

Result

AC

Duration

964ms

Code [DL]

use std::io::Read;fn main(){let mut b=String::new();std::io::stdin().read_to_string(&mut b);let mut x:Vec<i32>=b.trim().split(|c|c<'!').map(|e| e.parse().unwrap()).collect();for i in 0..9{x[i]-=x[9+i%3];}print!("{}",(x[0]*(x[5]*x[7]-x[4]*x[8])+x[1]*(x[3]*x[8]-x[5]*x[6])+x[2]*(x[4]*x[6]-x[3]*x[7]))/6);}

stdin

69 66 54
58 86 89
02 97 84
34 56 53

stdout

6021

stderr

warning: unused `std::result::Result` which must be used
 --> /tmp/code.rs:1:53
  |
1 | use std::io::Read;fn main(){let mut b=String::new();std::io::stdin().read_to_string(&mut b);let mut x:Vec<i32>=b.trim().split(|c|c<'!').map(|e| e.parse().unwrap()).collect();for i in 0..9{x[i]-=x[9+i%3];}print!("{}",(x[0]*(x[5]*x[7]-x[4]*x[8])+x[1]*(x[3]*x[8]-x[5]*x[6])+x[2]*(x[4]*x[6]-x[3]*x[7]))/6);}
  |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_must_use)] on by default

strace