void setup() {
  Serial.begin(9600);

  ADMUX |= B11000000;

  ADMUX |= B00000001;
}

void loop() {
  ADCSRA |= B11000000;
  
  while (bit_is_set(ADCSRA, ADSC));

  int val = ADCL | (ADCH << 8);
  
  Serial.println(val);
}