class Program
    {
        static BigInteger totalResult = new BigInteger(1);
        static object ForLock = 1;

        static void Main(string[] args)
        {
            int count;
            Console.WriteLine("Введите количество потоков >=1");
            count = Convert.ToInt32(Console.ReadLine());
            DateTime startTime = DateTime.Now;
            int a = 100000;
            List<Thread> threads = new List<Thread>();
            for (int i = count; i > 0; i--)
            {
                Thread th = new Thread(Fact);
                th.Name = (i).ToString();
                threads.Add(th);
                th.Start(new int[] { a, a - a / i });
                a -= a / i;
            }
            foreach (Thread th in threads)
            {
                th.Join();
            }
            Console.WriteLine("Все потоки завершились!");
            Console.WriteLine("Затрачено" + (startTime - DateTime.Now).ToString());
            Console.WriteLine("Результат - " + totalResult.ToString());
        }
        static void Fact(object param)
        {
            int start = (param as int[])[0];
            int end = (param as int[])[1];
            Console.WriteLine("[{0}] {1} - {2}", Thread.CurrentThread.Name, start, end);

            BigInteger res = new BigInteger(1);

            for (int b = start; b > end; b--)
            {
                res = res * b;
            }

            lock (ForLock)
            {
                totalResult *= res;
            }

            Console.WriteLine("Поток №{0} заврешился", Thread.CurrentThread.Name);
        }

    }
}