```
Sub x()
Dim v, i As Long
With Range("A1").CurrentRegion
v = .Value
.ClearContents
End With
For i = LBound(v, 1) To UBound(v, 1)
If v(i, 4) = "" Then
v(i, 4) = v(i, 2)
Else
v(i, 4) = v(i, 2) & " Sub " & v(i, 4)
End If
Next i
Range("A1").Resize(UBound(v, 1), 4) = v
End Sub
```