Sub aa()
Dim Coll As New Collection
Dim R As Range
Dim C As Range
Dim A$
Dim cpt&
'---
Set R = Selection
For Each C In R
On Error Resume Next
Coll.Add C, C
If Err <> 0 Then
cpt& = 0
Do
Err.Clear
cpt& = cpt& + 1
A$ = C & "." & cpt&
Coll.Add A$, A$
Loop Until Err = 0
C = Coll(Coll.Count)
End If
Next C
End Sub