void setup() {
  pinMode(0, OUTPUT);        // Set pin '0' to OUTPUT mode
  pinMode(3, INPUT_PULLUP);  // Set pin '3' to INPUT mode with pull-up
}

void loop() {
  while (digitalRead(3) == HIGH) {
    digitalWrite(0, HIGH);
    // What code needs to be added here to make the LED blink while button is pressed?
  }
  digitalWrite(0, LOW);
}