const byte buttonPin = 2;
const byte ledPin = LED_BUILTIN;
const unsigned long debounceMs = 30;
int lastReading = HIGH;
int stableState = HIGH;
unsigned long changedAt = 0;
bool ledState = false;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);
  Serial.begin(9600);
}

void loop() {
  const int reading = digitalRead(buttonPin);
  const unsigned long now = millis();
  if (reading != lastReading) changedAt = now;
  if (now - changedAt >= debounceMs && reading != stableState) {
    stableState = reading;
    if (stableState == LOW) {
      ledState = !ledState;
      digitalWrite(ledPin, ledState ? HIGH : LOW);
      Serial.println(ledState ? "On" : "Off");
    }
  }
  lastReading = reading;
}