how to mark all as read?

To: mutt-users <mutt-users@xxxxxxxx>
Subject: how to mark all as read?
From: "Chengqi(Lars) Song" <songcq@xxxxxxxxx>
Date: Mon, 5 Jan 2009 14:12:46 +0800
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hi,

i know how to do it step by step:
ctrl-t
~N <enter>
;N <enter>

but how to bind this function to a single key?

best
lars