Function AddStr(ByVal MyString As String) As String
If MyString = "z" Then
Return "aa"
Else
If Strings.Right(MyString, 1) = "z" Then
Return AddStr(Strings.Left(MyString, Len(MyString) - 1)) & "a"
Else
Return Strings.Left(MyString, Len(MyString) - 1) & Chr(Asc(Strings.Right(MyString, 1)) + 1)
End If
End If
End Function