[ Telerik C#] LOOPS - EX 13

// 13. * Write a program that calculates for given N how many trailing zeros present at the end of the number N!.
//  Examples:
//  N = 10 ---> N! = 3628800 ---> 2
//  N = 20 ---> N! = 2432902008176640000 ---> 4
//  Does your program work for N = 50 000?
//  Hint: The trailing zeros in N! are equal to the number of its prime divisors of value 5. Think why!

// 45:5=9, 9:5=1, значи 9+1=10 нули

using System;
using System.Numerics;

namespace ex13
{
    class Program
    {
        static void Main(string[] args)
        {
            int n;
            do
            {
                Console.Write("Enter N: ");
                n = Int32.Parse(Console.ReadLine());
            } while (!(n > 0));

            BigInteger nFact = 1;
            for (int i = 1; i <= n; i++)
            {
                nFact = nFact * i;
            }
            Console.WriteLine("{0}! = {1}",n,nFact);

            int zeroCounter = 0;
            while (true)
            {
                int result = n / 5;
                if (result != 0)
                {
                    zeroCounter = zeroCounter + result;
                    n = result;
                }
                else
                {
                    Console.WriteLine("Trailing zeros count: {0}", zeroCounter);
                    break;
                }
            }
        }
    }
}