#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,20,4);
void setup() {
lcd.init ();
lcd. backlight();
attachInterrupt(digitalPinToInterrupt (18), ISR_18, FALLING);
attachInterrupt(digitalPinToInterrupt(19), ISR_19, FALLING);
attachInterrupt(digitalPinToInterrupt (20), ISR_20, FALLING);
attachInterrupt(digitalPinToInterrupt (21), ISR_21, FALLING);

pinMode(18, INPUT_PULLUP);
pinMode(19, INPUT_PULLUP) ;
pinMode(20, INPUT_PULLUP);
pinMode(21, INPUT_PULLUP) ;
}

void loop() {
lcd.setCursor (0,0);
lcd.print (i);
lcd.print(":");
  

｝
void ISR_18()
{
void ISR_19()
｝
void ISR_20()
{
void ISR_21()

}