#define BUTTON_PIN PA3
#define LED_PIN PA3

int main(){
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);

  while(1){
    if (digitalRead(BUTTON_PIN)==LOW) {
      digitalWrite(LED_PIN, HIGH);
    }
    else {
      digitalWrite(LED_PIN, LOW);
    }
  }
}