void setup() {
  Serial.begin(9600);

  pinMode(0, INPUT);
  pinMode(1, INPUT);
  pinMode(2, INPUT);
  pinMode(3, INPUT);

  digitalWrite(0, LOW);
  digitalWrite(1, LOW);
  digitalWrite(2, LOW);
  digitalWrite(3, LOW);

}

void loop() {
  digitalWrite(0, HIGH);
  delay(500);
  digitalWrite(1, HIGH);
  delay(500);
  digitalWrite(2, HIGH);
  delay(500);
  digitalWrite(3, HIGH);
  delay(500);
  digitalWrite(3, LOW);
  delay(500);
  digitalWrite(2, LOW);
  delay(500);
  digitalWrite(1, LOW);
  delay(500);
  digitalWrite(0, LOW);
  delay(500);

}