#define MQ A5
#define RLED A4
#define GLED A2

void setup()
{
  Serial.begin(9600);
  pinMode(MQ, INPUT);
  pinMode(RLED, OUTPUT);
  pinMode(GLED, OUTPUT);
}

void loop()
{
  int smoke=analogRead(MQ);
  Serial.print("MQ: ");
  Serial.println(smoke);
  if(smoke>=800)
  {
    digitalWrite(RLED, HIGH);
    digitalWrite(GLED, LOW);
  }
  else
  {
    digitalWrite(RLED, LOW);
    digitalWrite(GLED, HIGH);
  }
}