Just 4.
I didn't even know they were doing it this weekend. I went to Wendy's and overheard some guy behind the counter telling his girlfriend it was "free Frosty day" and I figured he was just giving her special treatment. So I was like, (kind of sarcastically) "is it Free Frosty Day for ME too?" And he was like, "well, yeah."
I just figured he didn't want to get in trouble for giving his girlfriend one and not everyone else (I was the only other customer at the counter).
D'oh. I kinda figured it out once everyone else was strutting back to their table with 15 or so of them.
