Here you go:

Sub CopyDown()

Dim LR As Long, c As Long

LR = Range("E" & ActiveSheet.UsedRange.Rows.Count + 2).End(xlUp).Row

With Range("A2:D" & LR)
    On Error Resume Next
    .SpecialCells(xlCellTypeBlanks).FormulaR1C1 = "=R[-1]C"
    .Copy
    .PasteSpecial (xlPasteValues)
End With
End Sub