Change format from 2013-1 to 2013-01 in this function013

Dear Excel Forum members,

First of all, I want to thank you all for your big help with my former questions!

Today I have the following problem: One cell contains the following function:

=TEXT(C5, "yyyy")&-WEEKNUM(C5)

This function will transform a date from another cell, e.g. 01/02/2013 (Month/Day/Year) into the format 2013-1. But for further calculations I need the format like 2013-01.

I already tried several hours by myself to find the answer, but so far I had no success. Therefore, I hope someone could support me here!

Thanks and best regards