This looks like 100 or so, but there might be multiple exits and not sure when they started filming:
Bernie supporters having their signs CONFISCATED:
https://www.youtube.com/watch?v=2UcGn4SMHWg
Here’s another group walking out as a DNC operative tries to spin it:
http://fox8.com/2016/07/26/group-of-bernie-sanders-supporters-walks-out-of-dnc/