void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(27, OUTPUT);
  pinMode(25, OUTPUT);
  pinMode(21, OUTPUT);
  pinMode(18, OUTPUT);
}

void loop() {
  digitalWrite(27, HIGH);
  digitalWrite(21, HIGH);
  digitalWrite(25, LOW);
  digitalWrite(18, LOW);
  delay(1000);
  digitalWrite(25, HIGH);
  digitalWrite(18, HIGH);
  digitalWrite(27, LOW);
  digitalWrite(21, LOW);
  delay(1000);
}