Here is a related link

來源: 於 2009-11-29 13:30:03 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

http://web.wenxuecity.com/BBSView_archives.php?SubID=netiq&MsgID=118341&yr=2007

The link says it should have a limit. I estimated it for a few steps, it seems it >2. I think you need many more steps if you want it be close to 4.