void setup() {
  Serial.begin(9600);
  pinMode(2, OUTPUT);  
  pinMode(5, OUTPUT);  
  pinMode(3, OUTPUT);
}

void loop() {
int a=analogRead(A0);
Serial.println(a);
if(a>=789)
  {digitalWrite(3, HIGH);
  digitalWrite(2, LOW);
  digitalWrite(5, LOW);}

if(789>a>270)
  {digitalWrite(2, HIGH);
  digitalWrite(3, LOW);
  digitalWrite(5, LOW);}

if(270>=a)
  {digitalWrite(5, HIGH);
  digitalWrite(2, LOW);
  digitalWrite(3, LOW);}
}