"Subject To" property setup

I’m looking at how I should enter a rental property that I acquired “Subject To”? I am taking over somebody’s mortgage and need to know how to enter that. Is the Acquisition Price of the property the price I actually paid (for example, if I gave the seller 20k and am taking over his 100k mortgage it would only be 20k), or is it the total price that I would have paid if I bought the house outright (120k)?