g1smd - 4:25 pm on Jul 3, 2011 (gmt 0)
If those URLs rank, I would probably (at least initially) redirect those requests so you retain the traffic.
RewriteRule ^c/([^/]+)/([^/]+)/$ http://www.example.com/$2/ [R=301,L]
Once the old URLs are deindexed, I might simply block them using the 410 code.
RewriteRule ^c/([^/]+)/([^/]+)/$ - [G]