Option Explicit
Sub Essai()
Dim n&: n = Cells(Rows.Count, 1).End(3).Row: If n < 3 Then Exit Sub
Application.ScreenUpdating = 0: [A2].Resize(n - 1, 2).Sort [A2], 1
Dim i&
For i = n To 2 Step -1
With Cells(i - 1, 2)
If .Offset(1, -1) = .Offset(, -1) Then
.Value = .Value + .Offset(1): Rows(i).Delete
End If
End With
Next i
End Sub