int buttonPin = 9;
int ledPin = A1;
bool lastButtonState = HIGH;
bool outputState = false;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  bool buttonState = digitalRead(buttonPin);

  if (buttonState == LOW && lastButtonState == HIGH) {
    outputState = !outputState;
    digitalWrite(ledPin, outputState ? HIGH : LOW);
  }

  lastButtonState = buttonState;
}