Calculation of cost of acquisition for capital gain

Hi

I bought a under construction flat from builder where there was sale agreement of 12 lacs and a construction agreement of 36 lacs. So total cost which I paid was 48 lacs + stamp duty cost. Later on the final sale deed was done for a price of 22 lacs.

Now I am selling the flat at 54 lacs with same as sale deed value. Do I have to pay capital gain on 32 lacs(54-22) lacs or 6 lacs (54-48). Please advise.