int red=12,yellow=14,green=27;

void setup() {
  Serial.begin(115200);
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(green, OUTPUT);
}
void loop()
{
  switchOnLED(red);
  switchOnLED(yellow);

  switchOnLED(green);
}
void switchOnLED(int LED)
{
  digitalWrite(LED, HIGH);
  delay(3000); // 3 seconds delay
  digitalWrite(LED, LOW);
}