Cenvat input credit for taxable and exempted services

Hi

An entity is providing service to an Embassy ( Exempt from service tax ) which constitutes negligible percentage (1%) of the total services provided  . Remaining services are taxable and tax is being paid on it.Entity has only one registered office on which rent is being paid . 

My query is can the entity take entire input credit on the rent being paid or does it have to take propotionate input credit on the taxable service and for the exempted service ??

Thanks and regards

Mayank