const int redPin = 8; 
const int bluePin = 9; 

void setup() {

  pinMode(redPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void loop() {

  digitalWrite(redPin, HIGH);
  digitalWrite(bluePin, LOW);
  delay(500); 

 
  digitalWrite(redPin, LOW);
  digitalWrite(bluePin, HIGH);
  delay(500); 
}