excel fill in the gap

Sub test_v2()
    Dim i   As Long, j  As Long
    i = Cells(Rows.Count, "A").End(xlUp).Row
    Application.ScreenUpdating = False
    For j = i To 1 Step -1
        If Cells(j + 1, 1) <> "" Then
            If Cells(j + 1, 1).Value - Cells(j, 1).Value > 1 Then
                x = Cells(j + 1, 1).Value - Cells(j, 1).Value
                Rows(j + 1 & ":" & x + j - 1).Insert
            End If
        End If
    Next j
    With Range("A1:A" & Range("A" & Rows.Count).End(xlUp).Row)
        .Formula = "=Row()"
        .Value = .Value
    End With
    Application.ScreenUpdating = True
End Sub