#define LED_PIN 21
#define BUTTON_PIN 35

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(BUTTON_PIN)) {
    digitalWrite(LED_PIN, HIGH);
  }else{
    digitalWrite(LED_PIN, LOW);
  }
  delay(10); // this speeds up the simulation
}