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

void setup() {
  pinMode(RED, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(GREEN, OUTPUT);
}

void loop() {
  digitalWrite(RED, HIGH);
  digitalWrite(YELLOW, LOW);
  digitalWrite(GREEN, LOW);
  delay(3000);

  digitalWrite(RED, LOW);
  digitalWrite(YELLOW, HIGH);
  digitalWrite(GREEN, LOW);
  delay(1000);

  digitalWrite(RED, LOW);
  digitalWrite(YELLOW, LOW);
  digitalWrite(GREEN, HIGH);
  delay(3000);
}