const int trigPin = A1;
const int echoPin = A2;
int Motor1 = 13;
int Motor2 = 12;
int en1 = 11;
int en2 = 10;
int Motor3 = 9;
int Motor4 = 8;

void setup() {
Serial.begin(9600);
pinMode(Motor1,OUTPUT);
pinMode(Motor2,OUTPUT);
pinMode(Motor3,OUTPUT);
pinMode(Motor4,OUTPUT);
pinMode(en1,OUTPUT);
pinMode(en2,OUTPUT);
}

void loop() {
long duration, cm;

pinMode(trigPin, OUTPUT);
digitalWrite(trigPin, LOW);
delayMicrosecond(2);
digitalWrite(trigPin, HIGH);
delayMicrosecond(5);
digitalWrite(trigPin, LOW);

pinMode(echoPin, INPUT);
duration = pulseIn(echoPin, HIGH);

cm = microsecondsToCentimeters(duration);

Serial.print(cm);
Serial.print("cm");
serial.println();

delay(100);

if (cm<-40){
  digitalWrite(Motor1, LOW);
  digitalWrite(Motor2, HIGH);
  digitalWrite(Motor3, HIGH);
  digitalWrite(Motor4, LOW);
  digitalWrite(en1, 255);
  digitalWrite(en2, 255);
  }
else {
  digitalWrite(Motor1, LOW);
  digitalWrite(Motor2, HIGH);
  digitalWrite(Motor3, LOW);
  digitalWrite(Motor4, HIGH);
  digitalWrite(en1, 255);
  digitalWrite(en2, 255);
  }
}
long microsecondsToCentimeters(long microseconds) {
  return microsecond / 29 / 2;
}
}