#define LED_0 8
#define LED_1 9
#define LED_2 10
#define LED_3 11

void setup() {
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
}

void loop() {
  digitalWrite(LED_0, HIGH);
  delay(500);
  digitalWrite(LED_1, HIGH);
  delay(500);
  digitalWrite(LED_2, HIGH);
  delay(500);
  digitalWrite(LED_3, HIGH);
  delay(500);
  digitalWrite(LED_0, LOW);
  digitalWrite(LED_1, LOW);
  digitalWrite(LED_2, LOW);
  digitalWrite(LED_3, LOW);
  delay(500);
}