int red_led  =2;
int blue_led =3;
int green_led = 4;

void setup() {
  pinMode(red_led, OUTPUT);
  pinMode(blue_led, OUTPUT);
  pinMode(green_led, OUTPUT);
}

void loop() {

  digitalWrite(green_led, HIGH);
  delay(1000);
  digitalWrite(green_led, LOW);
  delay(1000);
  
}