void setup() {
  // put your setup code here, to run once:
pinMode(13 , OUTPUT);
pinMode(12 , OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
int LED ;

for (LED = 12 ; LED <= 13 ; LED++){
  digitalWrite(LED , HIGH);
    delay(500);
  digitalWrite(LED , LOW);
    delay(500);
}
}