Count of unique stores in a group

I have data with three columns,

Store #
Group Name
Item #

Every store # is associated to a particular Group Name, however a store # will appear more than once due to different Item # showing up. I'm trying to get the count of unique stores for each Group Name. I've attached a small sample file that hopefully gets the point across. I tried pivot tabling, but it would return the count every time a store showed up, even if it was the same one.