Help with inserting mulitple rows in worksheet

I am using this formula but it won't stop I want to do a range of A2:A300 inserting 12 rows in between them. the sheet already has employee names so i want 12 blank rows after name.

It works but I can't stop the loop!!!!

Sub test()    
Dim j As Long, r As Range    
j = InputBox("type the number of rows to be insered")    
Set r = Range("A2")    
Do    
Range(r.Offset(1, 0), r.Offset(j, 0)).EntireRow.Insert    
Set r = Cells(r.Row + j + 1, 1)    
MsgBox r.Address    
If r.Offset(1, 0) = "" Then Exit Do    
Loop    

End Sub

Thanks,

Nadia