Availment of cenvat credit on input service

The Facts of the case are:

A company "X" started the activity of construction of residential flats and construction activity is 

given on contract to another company "Y".

Here the "X' is not registered under the service tax law.

The "Y" is raising bills on work status and as per the agrement. 

"X" is paying the bills raised and accounting it as Work-in-Progress for the last one year.

Now "X" wants to collect advances from customers which is a taxable service and so gets registered now.

can "X'  claim input credit related to bills raised by "Y" before being registered to set off against taxable service.