void setup() {
  Serial.begin(9600);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
}

void loop() {
  Serial.println(analogRead(A0));

 if (analogRead(A0) < 500){
   digitalWrite(4, HIGH);
   digitalWrite(3,LOW);
 }

 if (analogRead(A0) > 500){
   digitalWrite(3, HIGH);
   digitalWrite(4,LOW);
 }

}