const int trigPin = 3;
const int echoPin = 2;
const int ledPin1 = 4;
const int ledPin2 = 5;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop() {
  int distance = readDistance();
  if (distance < 20) { // adjust the distance threshold
    digitalWrite(ledPin1, HIGH); // turn on red LED
    digitalWrite(ledPin2, LOW);
  } else if (distance < 50) { // adjust the distance threshold
    digitalWrite(ledPin1, LOW);
    digitalWrite(ledPin2, HIGH); // turn on green LED
  } else {
    digitalWrite(ledPin1, LOW);
    digitalWrite(ledPin2, LOW);
  }
}

int readDistance() {
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  int duration = pulseIn(echoPin, HIGH);
  int distance = duration * 0.034 / 2;
  return distance;
}