void setup() {pinMode(A0, OUTPUT);
digitalWrite(A0, HIGH);
  

}

  

void loop() { 
   for (int i = 2; i <  11; i = i +1 ) {
  digitalWrite(i, HIGH);
  delay(100);
  digitalWrite(i, LOW);
   }
    for (int i = 11; i >  2; i = i - 1) {
  digitalWrite(i, HIGH);
  delay(100);
  digitalWrite(i, LOW);
    }
  
}