Usage of standard functions into custom function (or user defined function)

I am using Microsoft excel 2010. I created my own customized function(or user defined function (UDF)).
I need to use existing function into UDF.
e.g.
Function MULTIPLYS(X As Variant, Y As Variant) As Long
MULTIPLYS = X * Y *2
MULTIPLYS = MOD(MULTIPLYS,2^16) 'need to use excel inbuilt function
End Function

Is it possible to use in-built excel function into UDF?
If yes then do we need to provide path of MOD excel function?
In above example, I am getting error"Compiler Error : Sub or Function not defined"

Thanks in advance.