class Who {

    // sample format:
    // system boot 2020-06-16 09:12
    private static final Pattern BOOT_FORMAT_AIX = Pattern.compile("\\D+(\\d{4}-\\d{2}-\\d{2})\\s+(\\d{2}:\\d{2}).*");
    private static final DateTimeFormatter BOOT_DATE_FORMAT_AIX = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm",
            Locale.ROOT);

    private Who() {
    }

    /**
     * Query {@code who -b} to get boot time
     *
     * @return Boot time in milliseconds since the epoch
     */
    public static long queryBootTime() {<FILL_FUNCTION_BODY>}
}

        String s = ExecutingCommand.getFirstAnswer("who -b");
        if (s.isEmpty()) {
            s = ExecutingCommand.getFirstAnswer("/usr/bin/who -b");
        }
        Matcher m = BOOT_FORMAT_AIX.matcher(s);
        if (m.matches()) {
            try {
                return LocalDateTime.parse(m.group(1) + " " + m.group(2), BOOT_DATE_FORMAT_AIX)
                        .atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
            } catch (DateTimeParseException | NullPointerException e) {
                // Shouldn't happen with regex matching
            }
        }
        return 0L;
    
<no_super_class>