#define BUTTON_PIN 2


int LED = 13;
int LEDState = LOW; 
byte lastButtonState;
unsigned long lastTimeButtonStateChanged = millis();
unsigned long debounceDuration = 50; //millis

void setup(){
  pinMode(LED, OUTPUT);
  pinMode(BUTTON_PIN, INPUT);
  lastButtonState = digitalRead(BUTTON_PIN);
}

void loop(){
  if ( millis() - lastTimeButtonStateChanged >= debounceDuration){
    byte buttonState = digitalRead(BUTTON_PIN);
    if (buttonState != lastButtonState){
      lastTimeButtonStateChanged = millis();
      lastButtonState = buttonState;

      if(buttonState == LOW){
        LEDState = !LEDState;
        digitalWrite(LED, LEDState);
      }
    }
  }
}