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

int ledState = LOW;
int buttonState;
int lastButtonState = LOW;

unsigned long lastDebounceTime = 0;
unsigned long debounceDelay = 20;
void setup() {
  pinMode(9, OUTPUT);
  pinMode(20, INPUT);
  digitalWrite(ledPin,ledState);
  Serial.begin(9600);
  Serial.println(buttonState);
}

void loop() {
  int reading = digitalRead(buttonPin);
  if(reading != lastButtonState){
    lastDebounceTime = millis();
  }
  if(millis()-lastDebounceTime > debounceDelay){
    if(reading != buttonState){
        buttonState = reading;
        if(buttonState == LOW){
          ledState = !ledState; 
        }
    }
  }
  digitalWrite(ledPin,ledState);

  lastButtonState = reading;
}