ub MaxItOut()

Dim x As Long
Dim MaxSlides As Long

MaxSlides = 100 ' or however far you want to take this
                ' Longs can take values up to 2,147,483,647
                ' Speaking of Long, it might take a LONG time to run the macro if you max it

' Assuming there's already one slide in the presentation
For x = 2 To MaxSlides
    ActivePresentation.Slides.Add x, ppLayoutBlank
    With ActivePresentation.Slides(x)
        With .Shapes.AddTextbox(msoTextOrientationHorizontal, 100, 100, 200, 200)
            .TextFrame.TextRange.Text = CStr(x)
        End With
    End With
Next x

End Sub