[dba-VB] (Free) C#/VB.NET equivalents of Excel.Application.WorksheetFunction.NormSDist(Arg1 As Double) As Double?

Hi All --

Do you know about any (free) equivalents of 

Exel.Application.WorksheetFunction.NormSDist(Arg1 As Double) As Double

?

I have got googled the following link:

http://bytes.com/topic/c-sharp/answers/240995-normal-distribution

but I'm not sure/have no time now to check will that simple solution be
equivalent to the Excel.Application.WorksheetFunction.NormSDist(...)?

I have to get developed an independent from MS Excel solution.

Thank you.

--
Shamil