unsigned char RED_LED = 23;

unsigned char YELLOW_LED = 19;

unsigned char GREEN_LED = 18;


void setup() {
  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  }

void loop() {

 digitalWrite(RED_LED, HIGH);
 digitalWrite(YELLOW_LED, HIGH);
 digitalWrite(GREEN_LED, HIGH);

 delay(2000);

 
 digitalWrite(RED_LED, LOW);
 digitalWrite(YELLOW_LED, LOW);
 digitalWrite(GREEN_LED, LOW);

 delay(2000);
}