// Complete the beautifulDays function below.
    static int beautifulDays(int i, int j, int k)
        {
            int days = 0;
            for (int start = i; start <= j; start++)
            {
                char[] reverse = start.ToString().ToCharArray();
                Array.Reverse(reverse);
                int rev = Convert.ToInt32(new string(reverse));
                if ((Math.Abs(start - rev) % k) == 0)
                {
                    days += 1;
                }
            }
            return days;
        }