Sub Mois_étudiés()
Dim plage As Range, pc As Byte, ad As String, i As Byte, n As Long
Set plage = [A5:A9] 'à adapter
plage.ClearContents 'RAZ
pc = Application.Min(plage.Count, 12) 'maxi 12
ad = plage.Address(0, 0)
For i = 1 To pc
1 n = Abs(Val(InputBox("Entrer le n° d'un mois :", _
pc & " mois différents à créer sur " & ad)))
If n = 0 Then Exit Sub
If n > 12 Or Application.CountIf(plage, n) Then GoTo 1
plage(i) = n
Next
End Sub