def main(field in1, field in2, field in3, field in4, field in5, field in6, field in7, field in8) -> (field):
  // first iteration
  field a = (in1 + in2) / 2
  field b = (in3 + in4) / 2
  field c = (in5 + in6) / 2
  field d = (in7 + in8) / 2
  field e = (in1 - in2) / 2
  field f = (in3 - in4) / 2
  field g = (in5 - in6) / 2
  field h = (in7 - in8) / 2
  // second iteration
  field i = (a + b) / 2
  field j = (c + d) / 2
  field k = (e - f) / 2
  field l = (g - h) / 2
  // third iteration
  field out1 = (i + j) / 2
  return (k - l) / 2