File Upload: Appending file name if it already exists

I've come across a number of solutions for doing this however none that have fit my needs yet.
I'm working on an application that when a picture is uploaded it is renamed something like this...
pic_2009_03_11_01.jpg
if this this already exists I want to append the "01" to "02" etc.  I know this mean I have to parse the file name without the extension somehow then convert it to an int then increment it by 1 however I'm not quite sure how to achieve this.  I'd prefer to do this in C# rather than with a javascript solution however I'd appreciate any suggestions if there is a better way.

thanks in advance!

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