using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Numerics;

​

namespace FactorialTrailingZeroes

{

    public class FactorialTrailinZero

    {

        public static void Main()

        {

            int numberInput = int.Parse(Console.ReadLine());

            calcFactorial(numberInput);

​

            BigInteger factorNum = calcFactorial(numberInput);

            BigInteger zero = countZero(factorNum);

​

            Console.WriteLine(zero);

        }

​

        private static BigInteger calcFactorial(int number)

        {

            BigInteger factorial = 1;

            for (int i = number; i >= 1; i--)

            {

                factorial = factorial * i;

            }

            return factorial;

        }

​

        private static BigInteger countZero(BigInteger factorial)

        {

            string numStr = Convert.ToString(factorial);

​

            int count = 0;

​

            for (int i = numStr.Length - 1; i >= 0; i--)

            {

                if(numStr[i].Equals('0'))

                {

                    count++;

                }

                else

                {

                    break;

                }

            }

            return count;

        }

    }

}