private long calculate()
        {
            int points = 1;
            long count = 1;
            bool goingUp = true;
            for (int i = 0; i < 20; i++)
            {
                if (goingUp)
                    count = count * (points++ * 2);
                else
                    count = count * (long)(points-- * 2);
                if (points == 20)
                    goingUp = !goingUp;
            }
            return count;
        }