void setup()
{
  pinMode(13, OUTPUT);
  pinMode(A0, INPUT);
  Serial.begin(9600);

}

void loop() {
  int a = analogRead(A0);
  Serial.println(a);
  if (a > 400)
  {
    digitalWrite(13, HIGH);
  }
  else
  {
    digitalWrite(13, LOW);
  }
}