const int analogPin = A0;

  

void setup() {
// put your setup code here, to run once:

pinMode(analogPin, OUTPUT);

}

  

void loop() {

// put your main code here, to run repeatedly:

int brightness;

  

for (brightness = 0; brightness <= 255; brightness += 5) {

analogWrite(analogPin, brightness);

delay(50);

}

  

for (brightness = 255; brightness >= 0; brightness -= 5) {

 analogWrite(analogPin, brightness);

 delay(50);

}

}