Update For Statement To Get Value Extracted From Filename

I have the following code which works fine;
For Each myFile As String In IO.Directory.GetFiles(Label1.Text, "*.zip")
Dim fi As New System.IO.FileInfo(myFile)
sFilename = fi.Name
Col_Prac_no = sFilename.Substring(1, sFilename.IndexOf("_") - 1)

For example: I have filename as:
I00018_20120329042035_111
The col_prac_no = 00018

Now, I want to update the for statement to have another value extracted from the filename.
The first letter of the filename. In the example:
I00018_20120329042035_111
The first letter of the filename in above example is I.

So if we have:
S00018_20120329042035_192
the value will be - S.