String finder(String s, int start, int currentMax) {
        if (s.length() - start <= currentMax)
            return null;

        int stop = start + currentMax - 1;
        for (int i = s.length() - 1; i > stop; i--) {
            if (isPalindorme(s, start, i)) {
                String next = finder(s, start + 1, i - start + 1);
                if (next == null)
                    return s.substring(start, i + 1);
                return next;
            }
        }
        String next = finder(s, start + 1, currentMax);
        if (next == null)
            return null;
        return next;
    }