How do I restore files accidentally deleted by the move operation in finder? I’m using Mavericks

Suppose we have the folder /a/photos which contains

/a/photos/jan
/a/photos/feb


And we have /b/photos which contains

/b/photos/mar


In the command prompt, if we write

mv /b/photos /a/photos


Then /a/photos will contain all of them (merge):

/a/photos/jan
/a/photos/feb
/a/photos/mar


However, I did the move operation in Finder (command+c, command+alt+v) and pressed the “overwrite” button thinking it has the same behavior as in mv

Now all my original files in /a/photos are lost. The only thing remaining is:

/a/photos/mar


How do I recover it?

Thanks a lot
STOP ALL FILE OPERATIONS AND UNMOUNT YOUR HARD DRIVE

If you haven't written to the Drive since then, it will eventually save you.

When Moving files like this, they get marked as deleted on the drive.
Therefore you can only try to recover them.

Which means: 


Get a Recovery-Software like DataRescue
Or a free (CLI) programm like PhotoRec
Try recovering the files.