Private Sub Workbook_Open()
Dim a, b As Integer
a = ActiveSheet.Index
b = 0
For Each ws In Worksheets
If ws.Name Like "IW##" Then
If CInt(Right(ws.Name, 2)) > b Then
b = CInt(Right(ws.Name, 2))
a = ws.Index
End If
End If
Next ws
Sheets(a).Select
End Sub