Naming of directory problem

hi all
suppose in particular directory i have lots of directory supoose
201009 201010 201011 201012
now by mistake i have rename all these directory as
201009.bk 201010.bk 201011.bk 201012.bk

now how can i revert the changes back

pls help me regarding this

for d in *.bk/; do
  mv -- "$d" "${d%.bk/}"
done  

thanx man it worked