int RED = 5;
int YELLOW = 18;
int GREEN = 19;


void setup() {
  pinMode(5, OUTPUT);   // RED
  pinMode(18, OUTPUT);  // YELLOW
  pinMode(19, OUTPUT);  // GREEN
}

void loop() {
  digitalWrite(5, HIGH);
  digitalWrite(18, LOW);
  digitalWrite(19, LOW);
  delay(3000);

  digitalWrite(5, LOW);
  digitalWrite(18, HIGH);
  digitalWrite(19, LOW);
  delay(1000);

  digitalWrite(5, LOW);
  digitalWrite(18, LOW);
  digitalWrite(19, HIGH);
  delay(3000);
}