Sub macro()
Dim i As Long
Application.ScreenUpdating = False
For i = 1 To ActiveSheet.UsedRange.Rows.Count
Cells(i, 1) = _
DateSerial(Cells(i, 1).Offset(, 2), Cells(i, 1).Offset(, 1), Cells(i, 1))
Cells(i, 2).Resize(1, 2).Clear
Next
Application.ScreenUpdating = True
End Sub