// 1.3
int ledPin1 = D3;
int ledPin2 = D2;

void setup() {
  // We want to tell the Argon that we'll use
  // D3 as an output pin.
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop() {
    digitalWrite(ledPin1, HIGH);   
    digitalWrite(ledPin2, LOW);
    delay(500); 
    digitalWrite(ledPin2, HIGH);   
    digitalWrite(ledPin1, LOW);
    delay(500); 
}