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

}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(3, HIGH);
delay(200);
digitalWrite(4, LOW);
delay(200);
digitalWrite(4, HIGH);
delay(200);
digitalWrite(3, LOW);
delay(200);

}