int trigger=4;
int echo=5;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
 
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(23, OUTPUT);//green
  pinMode(22, OUTPUT);//yellow
  pinMode(21, OUTPUT);//red
}

int finding_distance(){
  digitalWrite(trigger, HIGH);
  delay(100);
  digitalWrite(trigger, LOW);
  float a=pulseIn(echo, HIGH);
  return(a*0.034/2);
}
void loop() {
  int distance=finding_distance();
  Serial.println(distance);
  if(distance>300){
  Serial.println("safe");
  digitalWrite(23, HIGH);
  digitalWrite(21, LOW);
  digitalWrite(22, LOW);}
  else if(200<=distance && distance<300){
  Serial.println("unsafe");
  digitalWrite(22, HIGH);
  digitalWrite(23, LOW);
  digitalWrite(21, LOW);
  }
  else if(distance<200){
    Serial.println("danger");
    digitalWrite(21, HIGH);
    digitalWrite(22, LOW);
    digitalWrite(23, LOW);
}
  
    // put your main code here, to run repeatedly:
   // this speeds up the simulation
}