if (!isDigits(s)) {
            return null;
        }

        try {
            long longValue = Long.parseLong(s);
            if (longValue > Integer.MAX_VALUE) {
                return null;
            }
            return (int) longValue;
        } catch (NumberFormatException e) {
            // should never happen since checked isDigits(s) before
            return null;

        }
    }

    private static Item parseItem(boolean isDigit, String buf) {
        return parseItem(false, isDigit, buf);
    }

    private static Item parseItem(boolean isCombination, boolean isDigit, String buf) {
        if (isCombination) {
            return new CombinationItem(buf.replace("-", ""));
        } else if (isDigit) {
            buf = stripLeadingZeroes(buf);