static bool IsPolindrom(string num)
        {
            for (int i = 0, j = num.Length - 1; i <= j; i++, j--)
                if (num[i] != num[j])
                    return false;
            return true;
        }

        static string ToBinary(int num)
        {
            int x = (num % 2);
            num /= 2;
            if (num == 0)
                return x.ToString();
            return ToBinary(num) + x.ToString();
        }