int ledPinR = D2;
int ledPinB = D3;

void setup() {
  pinMode(ledPinR, OUTPUT);
  pinMode(ledPinB, OUTPUT);
}

void loop() {

  // Exercise 3
  digitalWrite(ledPinR, HIGH); 
  digitalWrite(ledPinB, LOW);
  delay(1000);              
  digitalWrite(ledPinB, HIGH);
  digitalWrite(ledPinR, LOW);
  delay(1000);            

}