void setup() {
  pinMode(A0, INPUT);
  pinMode(2, INPUT);
  pinMode(3, INPUT);
  pinMode(4, INPUT);
  Serial.begin(9600);
}

void loop() {
  int a = analogRead(A0);

  int pwm = map (a, 0, 1023, 0, 255);
  analogWrite(2, pwm);

  if(a >= 0 && a <= 33)
  {
    digitalWrite(4, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(2, LOW);
  }
  else if (a >= 34 && a <= 66)
  {
    digitalWrite(4, LOW);
    digitalWrite(3, HIGH);
    digitalWrite(2, LOW);
  }
  else if (a >= 67 && a <= 99)
  {
    digitalWrite(4, LOW);
    digitalWrite(3, LOW);
    digitalWrite(2, HIGH);
  }
  else 
  {
    digitalWrite(4, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(2, HIGH);
    delay(100);
    digitalWrite(4, LOW);
    digitalWrite(3, LOW);
    digitalWrite(2, LOW);
  }
}