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

  pinMode(18, INPUT_PULLUP);
  pinMode(19, INPUT_PULLUP);
  pinMode(21, INPUT_PULLUP);
}

void loop() {

  if (digitalRead(18) == LOW) {
    Serial.println("BOTON 1");
  }

  if (digitalRead(19) == LOW) {
    Serial.println("BOTON 2");
  }

  if (digitalRead(21) == LOW) {
    Serial.println("BOTON 3");
  }

  delay(200);
}