const int ledPin = 5; 

void setup() {
  pinMode(ledPin, OUTPUT); 
}

void loop() {
  // Gradually increase brightness
  for (int brightness = 0; brightness <= 255; brightness += 5) {
    analogWrite(ledPin, brightness);
    delay(10); 
  }

  // Gradually decrease brightness
  for (int brightness = 255; brightness >= 0; brightness -= 5) {
    analogWrite(ledPin, brightness);
    delay(10); 
  }
}