int red = 2;
int yellow= 4;
int green= 12;

void setup() {

  pinMode(red, OUTPUT);
  digitalWrite(red, LOW);
  pinMode(yellow, OUTPUT);
  digitalWrite(yellow, LOW);
  pinMode(green, OUTPUT);
  digitalWrite(green, LOW);

}

void loop() {
  digitalWrite(red, HIGH);
  delay(5000);
  digitalWrite(red, LOW);
  digitalWrite(yellow, HIGH);
  delay(5000);
  digitalWrite(yellow, LOW);
  digitalWrite(green, HIGH);
  delay(5000);
  digitalWrite(green, LOW);
}