int buttonPin = D9;
int Led = A4;
int buttonState;
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(Led, OUTPUT);
  pinMode(buttonPin, INPUT);
}

// the loop function runs over and over again forever
void loop() {
  buttonState = digitalRead(buttonPin);
  if (buttonState == LOW) {
    digitalWrite(Led, HIGH);

  } else {
    digitalWrite(Led, LOW);
  }
  
}