18.ZeroCounter

using System;

class Program
{
    static void Main()
    {
        long num = long.Parse(Console.ReadLine());
        long zeroSum = 0;
        long k = 1;

        while (Math.Pow(5, k) < num)
        {
            long powResult = (long)Math.Pow((double)5, k);
            zeroSum += num / powResult;
            k++;
        }
        Console.WriteLine("Number of zeros: {0}", zeroSum);
    }
}