int sensorState = 0;

void setup()
{
  pinMode(4, INPUT);             
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop()
{
  sensorState = digitalRead(4);  

  if (sensorState == HIGH) {
    digitalWrite(LED_BUILTIN, HIGH);
  } else {
    digitalWrite(LED_BUILTIN, LOW);
  }

  delay(10);
}