void setup() {
  pinMode(8, INPUT_PULLUP);
  pinMode(13, OUTPUT);
  digitalWrite(13, LOW);

  Serial.begin(9600);
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:
  if(Serial.available()) {
    char data_rcvd = Serial.read();

    if(data_rcvd == '1') digitalWrite(13, HIGH);
    if(data_rcvd == '0') digitalWrite(13, LOW);
  }

  if(digitalRead(8)==HIGH) Serial.write('0');
  else Serial.write('1');
}