Purchase consideration of property

My father purchased a property in 1977 by Rs 2500/- only and I have only a piece of paper. We sold this property in February,2023 without revaluation by a Registered valuer but ascertain the value by searching in the wbregistration.gov.in portal and found that the current value of the property is Rs.46.00 lacs and sold it
by Rs.70.00 lacs.

My query is that, "How much I consider the cost of acquisition while calculating the Capital Gain"?

pls advice.