// LEDs are connected to digital pins D4 and D15
const int ledPin1 = 4;
const int ledPin2 = 15;

void setup(){
  // Initialize the digital pins as outputs
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop() 
{
  // Turn first LED ON and second LED OFF
  digitalWrite(ledPin1, HIGH);
  digitalWrite(ledPin2, LOW);
  delay(1000);  // Wait for 1 second

  // Turn first LED OFF and second LED ON
  digitalWrite(ledPin1, LOW);
  digitalWrite(ledPin2, HIGH);
  delay(1000);  // Wait for 1 second
}