#include <Servo.h>

Servo myservo;
const int trigPin = 9;
const int echoPin = 10;

void setup() {
  myservo.attach(3);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH);
  int distance = duration * 0.034 / 2;

  if (distance < 50) {
    myservo.write(180);
  } else {
    myservo.write(0);
  }
  delay(100);
}