// LED Pins
const int redLED = 13;
const int greenLED = 12;
const int blueLED = 11;
const int yellowLED = 10;

void setup() {
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(blueLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
}

void loop() {
  // Red ON
  digitalWrite(redLED, HIGH);
  delay(500);
  digitalWrite(redLED, LOW);

  // Green ON
  digitalWrite(greenLED, HIGH);
  delay(500);
  digitalWrite(greenLED, LOW);

  // Blue ON
  digitalWrite(blueLED, HIGH);
  delay(500);
  digitalWrite(blueLED, LOW);

  // Yellow ON
  digitalWrite(yellowLED, HIGH);
  delay(500);
  digitalWrite(yellowLED, LOW);
}