local modem = peripheral.wrap("top")
modem.open(42)

while true do
  local event, peripheral_name, channel, replyChannel, message, distance = os.pullEvent("modem_message")
  print("Received a message on channel", channel, "at", distance, "blocks away.")
  print("The message: ", message)
  modem.transmit(43, 42, distance)
end