Modify the day of the date field based on another field

Hi All -

I have two fields in my report.

Field 1 - Day of the months (1,2,3,4,5,6,...28,29,30)

Field 2 - Date field.

I want to create a variable based on these two fields so that I capture year and month from the Field 2 and the Day from the Field 1.

Example:

Field 1 - 14

Field 2 - 12/18/2013 (mm/dd/yyyy)

I want my variable to be displayed as 12/14/2013

How can we achieve this? Any help is appreciated.

I am using SAP BI Web Intelligence 4.0