FactorialExample

using System;
using System.Numerics;


class PrimeCheck
{
    static void Main()
    {
        DateTime startTime = DateTime.Now;
        Console.Write("n = ");
        int n = Convert.ToInt32(Console.ReadLine());
        // Calculate n! =
        BigInteger result = 1;
        while (true)
        {
            Console.Write(n);
            if (n==1)
            {
                break; // kato stignem do 1 se mahame ot cikula
            }
            Console.Write(" * ");
            checked
            {
                result = result * n;
            }
            n--;
        }
        Console.WriteLine(" = {0}", result);
        DateTime finishtTime = DateTime.Now;
        Console.WriteLine(finishtTime-startTime);
    }
}