const byte LEFT_EYE = 3;
const byte RIGHT_EYE = 10;
const unsigned long STEP_MS = 4;
void setup() {
  pinMode(LEFT_EYE, OUTPUT);
  pinMode(RIGHT_EYE, OUTPUT);
}
void loop() {
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(LEFT_EYE, brightness);
    analogWrite(RIGHT_EYE, brightness);
    delay(STEP_MS);
  }
  for (int brightness = 254; brightness >= 1; brightness--) {
    analogWrite(LEFT_EYE, brightness);
    analogWrite(RIGHT_EYE, brightness);
    delay(STEP_MS);
  }
}