main :: IO ()
main = do
  hSetBinaryMode stdin True
  hSetBinaryMode stdout True
  bsIn <- C.getContents
  let hexBs = C.filter (isHexDigit) bsIn
  B.putStr $ B.pack $ unhex hexBs
main :: IO ()
main = do
  hSetBinaryMode stdin True
  hSetBinaryMode stdout True
  bsIn <- C.getContents
  let hexBs = C.filter (isHexDigit) bsIn
  B.putStr $ B.pack $ unhex hexBs
main = do
  hSetBinaryMode stdin True
  hSetBinaryMode stdout True
  bsIn <- C.getContents
  let hexBs = C.filter (isHexDigit) bsIn
  B.putStr $ B.pack $ unhex hexBs