int redLED = 13;    
int yellowLED = 12; 
int greenLED = 11; 

void setup() {
  pinMode(redLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
}

void loop(){
  digitalWrite(redLED, HIGH);
  delay(2000); 

  digitalWrite(redLED, LOW);
  digitalWrite(yellowLED, HIGH);
  delay(1000);

  digitalWrite(yellowLED, LOW);
  digitalWrite(greenLED, HIGH);
  delay(2000);

  digitalWrite(greenLED, LOW);
  digitalWrite(yellowLED, HIGH);
  delay(1000);

  digitalWrite(yellowLED, LOW);
}