#include <LiquidCrystal.h>

int val = 0;
int prevVal = 0;
int pin = 2;
int n = 0;
LiquidCrystal lcd(8,9,4,5,6,7);

void setup(){
  lcd.begin(16, 2);
  pinMode(pin, INPUT);
  val = digitalRead(pin);
  prevVal = digitalRead(pin);
}

void loop(){
  val = digitalRead(pin);
  if(val != prevVal){
    prevVal = val;
    lcd.setCursor(0, 0);
    lcd.print(++n / 2);
  }
}