regex pattern assistance

Hi,
Can anyone please assist.

given the string

x<-"/mnt/AO/AO Data/S01-012/120824/"

I would like to extract "S01-012"

require(stringr)

str_match(x,"\\/mnt\\/AO\\/AO Data\\/(.+)\\/+")
str_match(x,"\\/mnt\\/AO\\/AO Data\\/(\\w+)\\/+")

both nearly work. I expected I would use something like:

str_match(x,"\\/mnt\\/AO\\/AO Data\\/([\\w -]+)\\/+")

but I don't seem able to get the square bracket grouping to work
correctly. Can someone please show me where I am going wrong?

Thanks,
Tom