Accounting for purchases made by composition dealer

Dear Sir/Madam,

    I likes to know  accounting entries for purchases made by composition deal purchased from registered regular dealer.

   He(Composition dealer)  purchased goods for Rs.1,00,000/- and paid Rs.1,18,000/- including CGST Rs.9,000/- & SGST Rs.9,000/-. How can I treat the total GST Payment of Rs.18,000/-, weather I considered as Purchase cost and including in purchases or can i take as indirect expenses of this Rs.18,000/- 

Thanking you