Contar los Meses Sin Ventas

[#1]

Hi Everybody, I need to make a Pivot Table and it´s must calculate like a filter the cuantity of month without sales.

ejample

Itemcode  Venta Period

1-1             0       01-2013

1-2            1000   02-2013

1-3            1100   02-2013

y I need like as

itemcode    01-2013    02-1013              Expresion

1-1              0                  0                  Count(if(Period <>0))

1-2              0                  01

1-3              0                  01