void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(1, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
}

// the loop function runs over and over again forever
void loop()
{
digitalWrite(1, HIGH);
delay(500);
digitalWrite(2, HIGH);
delay(500);
digitalWrite(1, LOW);
digitalWrite(3, HIGH);
delay(500);
digitalWrite(2, LOW);
digitalWrite(1, HIGH);
delay(500);
digitalWrite(3, LOW);
}