// Define the pins for the LEDs
const int led1 = 13;
const int led2 = 11;
const int led3 = 9;

void setup() {
  // Set the LED pins as output
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
}

void loop() {
  // Turn on LED1 and wait for 500 milliseconds
  digitalWrite(led1, HIGH);
  delay(500);
  // Turn off LED1
  digitalWrite(led1, LOW);
  
  // Turn on LED2 and wait for 500 milliseconds
  digitalWrite(led2, HIGH);
  delay(500);
  // Turn off LED2
  digitalWrite(led2, LOW);
  
  // Turn on LED3 and wait for 500 milliseconds
  digitalWrite(led3, HIGH);
  delay(500);
  // Turn off LED3
  digitalWrite(led3, LOW);
}