// Sequential Blink for 4 LEDs - 2, 3, 4, 5

const int LED_COUNT = 4;
const int LED_PINS[LED_COUNT] = {2, 3, 4, 5};  

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

void loop() {
  
  for (int i = 0; i < LED_COUNT; i++) {
    digitalWrite(LED_PINS[i], HIGH);  
    delay(500);                     
    digitalWrite(LED_PINS[i], LOW);   
  }
 
  for (int i = LED_COUNT-2; i > 0; i--) {  
    digitalWrite(LED_PINS[i], HIGH);
    delay(500);
    digitalWrite(LED_PINS[i], LOW);
  }
}