Default folder deleted - can not change back keybinding theme

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http://askubuntu.com – I accidently removed Default folder from /usr/share/themes and now can not change the Keybindig theme back to default under advanced setting -> theme. Default option is simply gone, not there anymore. Couldn't get it back... I am using Ubuntu 12.04 with Gnome shell. Any thoughts on what can bring this option back? Thanks! (HowTos)