#include <math.h>
#include <LiquidCrystal_I2C.h>
#define TRIG 3
#define ECHO 2
#define SPEED_OF_SOUND 0.0343
unsigned long duration;
unsigned long distance;
LiquidCrystal_I2C lcd(0x27, 16, 2);
void setup()
{
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);

  lcd.init();
  lcd.backlight();
  lcd.begin(16, 2);
  lcd.clear();
}
void loop()
{
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  duration = pulseIn(ECHO, HIGH);
  distance = round(duration * SPEED_OF_SOUND * 0.5);
  lcd.print(distance);
  lcd.print("cm");
  lcd.setCursor(0,1);
  lcd.print(distance < 20 ? "danger" : "safe");
  lcd.setCursor(0,0);
}