// Define LED pin numbers 
const int redLED = 2; 
const int yellowLED = 3;
const int greenLED = 4;

void setup() {
 // Initialize LED pins as OUTPUT 
 pinMode(redLED, OUTPUT); 
 pinMode(yellowLED, OUTPUT); 
 pinMode(greenLED, OUTPUT);
}

void loop() {
 // Red light
 digitalWrite(redLED, HIGH); 
 digitalWrite(yellowLED, LOW); 
 digitalWrite(greenLED, LOW); 
 delay(2000); // 2 seconds

 // Red and yellow lights 
 digitalWrite(redLED, HIGH);
 digitalWrite(yellowLED, HIGH); 
 digitalWrite(greenLED, LOW); 
 delay(1000); // 1 second

 // Green light
 digitalWrite(redLED, LOW);
 digitalWrite(yellowLED, LOW);
 digitalWrite(greenLED, HIGH);
 delay(2000); // 2 seconds

 // Yellow light
 digitalWrite(redLED, LOW); 
 digitalWrite(yellowLED, HIGH);
 digitalWrite(greenLED, LOW); 
 delay(1000); // 1 second
}