Sub Ajoute()
Dim lig As Long
lig = [C65536].End(xlUp).Row
Rows(lig).Copy Rows(lig + 1)
Rows(lig + 1).ClearContents
Range("C" & lig + 1) = [A3]
End Sub
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$A$3" Then Ajoute
End Sub