a = 4.times.map{gt.split.map{|s|s.toi}} v = 9.times.map{|i| a[i/3+1][i%3]-a[0][i%3]} p (v[0]*(v[4]*v[8]-v[5]*v[7])+v[1]*(v[5]*v[6]-v[3]*v[8])+v[2]*(v[3]*v[7]-v[4]*v[6]))/6