Sub test()
Dim Semaine As Range, Cell As Range, Col As Integer
For Each Cell In Range("C4:C55")
Set Semaine = Union([U4:U20], [AA4:AA18], [AG4:AG31]).Find(Cell.Value, LookIn:=xlValues, lookat:=xlWhole)
If Not Semaine Is Nothing Then
Col = Semaine.Column
Select Case Col
Case 21: Cell.Offset(0, 12).Value = [Y22].Value
Case 27: Cell.Offset(0, 12).Value = [AE20].Value
Case 33: Cell.Offset(0, 12).Value = [AK33].Value
End Select
End If
Next
End Sub