const int LED1 = D0;
const int LED2 = D1;
const int LED3 = D2;

void setup() {
  pinMode(LED1, OUTPUT); 
  pinMode(LED2, OUTPUT); 
  pinMode(LED3, OUTPUT); 
}

void loop() {
  digitalWrite(LED1, HIGH); // turns on LED 1
  delay(1000); // wait 1 sec
  digitalWrite(LED1, LOW); // turns off LED 1

  digitalWrite(LED2, HIGH); // turns on LED 2
  delay(1000); // wait 1 sec
  digitalWrite(LED2, LOW); // turns off LED 2

  digitalWrite(LED3, HIGH); // turns on el LED 3
  delay(1000); // wait 1 sec
  digitalWrite(LED3, LOW); // Aturns off LED 3
}