void setup() {
  // put your setup code here, to run once:
  pinMode(D0, OUTPUT);
  pinMode(D1, OUTPUT);
  pinMode(D2, OUTPUT);
  pinMode(D3, OUTPUT);
  pinMode(D4, INPUT);
  pinMode(D5, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(D0, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D3, LOW);
  delay(500);

  digitalWrite(D0, LOW);
  digitalWrite(D1, HIGH);
  digitalWrite(D2, LOW);
  digitalWrite(D3, LOW);
  delay(500);
  
  digitalWrite(D0, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D2, HIGH);
  digitalWrite(D3, LOW);
  delay(500);
  
  digitalWrite(D0, LOW);
  digitalWrite(D1, LOW);
  digitalWrite(D2, LOW);
  digitalWrite(D3, HIGH);
  delay(500);
}