Adding Numbers not working

Hi at all,
i want to add the Number 40000 to the filenames, for example:

Filename old: 1.doc
Filename new: 400001.doc

Filename old: 10.doc
Filename new: 400010.doc

Filename old: 12345.doc
Filename new: 412345.doc


Filename old: 100000.doc
Filename new: 500000.doc

the following script doesn't work:

var
dokumentid_alt = item.newBasename
dokumentid_neu = dokumentid_alt+400000;

return dokumentid_neu;


can someone help me please?
thanks

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