unsigned char count;

void setup() {
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
  count = 10;
}

void loop() {
  digitalWrite(count, HIGH);
  delay(2000);
  digitalWrite(count, LOW);
  count++;
  if(count > 13) {
    count = 10;
  }
}