Potential Closing Date | Close Month Coversion

Potential Closing Date | Close Month Coversion

Do you know what formula would return a Potential Closing Date as follows (in a date format)?

<month number>/1/<year>

A few examples:

Closing Date: 11/15/2013 ---> Closing Month: 11/1/2013
Closing Date: 12/20/2013 ---> Closing Month: 12/1/2013

Thanks for any help you can provide