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