int pin[] = {15, 4, 5, 18};

void setup() {
  for (int i = 0; i <= 3; i++) {
  pinMode(pin[i], OUTPUT);
  }
}

void loop() {
  for (int i = 0; i <= 3; i++) {
  digitalWrite(pin[i], HIGH);
  digitalWrite(pin[i], 0);
  delay(1000);
  }
  
  

}