int a = 13;
int b = 12;
void setup() {
  pinMode(a, OUTPUT);
  pinMode(b, OUTPUT);

}

void loop() {
  digitalWrite(a, HIGH);
  delay(500);
  digitalWrite(a, HIGH);
  delay(500);
  digitalWrite(b, LOW);
  delay(500);
  digitalWrite(b, LOW);
  delay(500);

}