#define BUTTON_A  3
#define LED_A     13

void setup() {
  Serial.begin(115200);

  pinMode(BUTTON_A, INPUT);
  pinMode(LED_A, OUTPUT);
}

int button_a = 0;

void loop() {
  button_a = digitalRead(BUTTON_A);

  if (button_a == LOW) {
    Serial.println("Button Clicked!");
  }
}