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Hm, X Input is an ApI that is needed for the X Box 360 controller.
The error message aside, re-downloading the game is really easy. Just go to the game's page in your library and download it. Done.

If Galaxy acts up for some reason, just download the offline installer.
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zlaywal: I could only suggest to install DirectX End-User Runtime Web Installer here:

https://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=35
...or use standalone version (it's a matter of preference)

https://www.microsoft.com/en-us/download/details.aspx?id=8109