const int B = 12, L = 0;
bool started = 0;

void setup() {
  pinMode(B, INPUT_PULLUP);
  pinMode(L, OUTPUT);
}

void loop() {
  bool pressed = !digitalRead(B);
  if (pressed) started = 1; // Unlock the LED after first touch

  if (started) {
    digitalWrite(L, pressed); // LED is ON only while button is LOW
  }
}