void setup() {
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(2, INPUT); 
}

void loop() {
  int switchState = digitalRead(2); 

  if (switchState == HIGH) {
    for (int i = 11; i <= 13; i++) {
      digitalWrite(i, HIGH);
      delay(1000);
      digitalWrite(i, LOW);
      delay(1000);
    }
  } else {
    for (int i = 13; i >= 11; i--) {
      digitalWrite(i, HIGH);
      delay(1000);
      digitalWrite(i, LOW);
      delay(1000);
    }
  }
}