void setup() {
  pinMode(13, OUTPUT);
  pinMode(9, INPUT);
}

int l, pl;
uint32_t longPressStart = 0;
bool longPressCanStart = true;
bool b;

void loop() {
  l = digitalRead(9);

  if (l < pl) longPressStart = millis();
  else if (pl < l) longPressCanStart = true;

  if (!l && (millis() - longPressStart) > 1000 && longPressCanStart) {
    longPressStart = millis(); b = !b; longPressCanStart = false;
  }

  digitalWrite(13, b);

  pl = l;
}