const int ledPin = 9;
const int buttonPin = 20;

void setup() {
  pinMode(9, OUTPUT);
  pinMode(20, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  int buttonState = digitalRead(buttonPin);
    if(buttonState == HIGH){
      digitalWrite(ledPin, LOW);
    }
    else{
      digitalWrite(ledPin,HIGH);
    }
  
  Serial.println(buttonState);
}