void setup() {
  // put your setup code here, to run once:
pinMode(2, OUTPUT);
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(4, 1);
  delay(2000);
  digitalWrite(4, 0);
  digitalWrite(3, 1);
  delay(2000);
  digitalWrite(3,0);
  digitalWrite(2, 1);
  delay(2000);
  digitalWrite(2,0);
}