#define BTN_PIN 4
#define LED_PIN 2

void setup() {
  pinMode(BTN_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  bool button = digitalRead(BTN_PIN);
  bool led_on = digitalRead(LED_PIN);
  digitalWrite(LED_PIN, button ? LOW : !led_on);
  Serial.println("LED " + String(button ? "OFF" : (led_on ? "OFF" : "ON")));
  delay(500);
}