strange ps(1) output

["FUKAUMI Naoki" <fun%naobsd.org@localhost>]

Hi,

% uname -a
NetBSD ea65.naobsd.org 2.0E NetBSD 2.0E (XEN) #0: Sat May  8 17:24:16 JST 2004
 fun%ea65.naobsd.org@localhost:/home/fun/src/sys/arch/xen/compile/XEN i386
% ps ax
PID TT STAT    TIME COMMAND
  0 ?? DKs  -18067156:-23.83 [swapper]
  1 ?? Is   0:00.01 init
  2 ?? DK   0:00.00 [pms0]
  3 ?? DK   0:00.00 [xbdupdate]
  4 ?? DK   -18067156:-23.83 [pagedaemon]
  5 ?? DK   -18067156:-23.88 [ioflush]
  6 ?? DK   -18067156:-23.84 [aiodoned]
180 ?? Is   0:00.01 /usr/sbin/syslogd -s
(snip)

What is "-18067156:"?

--
FUKAUMI Naoki