int led1 = D2;
int led2 = D3;

void setup() {
  // We want to tell the Argon that we'll use
  // D2 as an output pin.
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);

}

void loop() {
    
    for(int i = 0; i < 5; i++) {
        digitalWrite(led1, HIGH);
        digitalWrite(led2, LOW);
        delay (500);
        
        digitalWrite(led1, LOW);
        digitalWrite(led2, HIGH);
        delay (500);
    }
    
    delay(3000);
}