#define LED_PIN     PA5
#define BUTTON_PIN  PC13   // Active LOW

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP); // Internal pull-up

  Serial.begin(9600);   // Start Serial Monitor
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    digitalWrite(LED_PIN, HIGH);   // LED ON
    Serial.println("LED ON");
  } else {
    digitalWrite(LED_PIN, LOW);    // LED OFF
    Serial.println("LED OFF");
  }

  delay(2000); // small delay to avoid message flooding
}