using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Numerics;

namespace Problem_13.Trailing_Zeroes_in_N_
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            BigInteger fact = 1;

            for (int i = 1; i <= n; i++)
            {
                fact *= i;
            }

            bool end = true;
            int zeros = 0;
            while(end == true)
            {
                if(fact % 10 == 0)
                {
                    fact /= 10;
                    zeros++;
                }
                else
                {
                    end = false;
                }
            }

            Console.WriteLine(zeros);


        }
    }
}