Finding Psuedo $R^2$ values from positive log-likelihood

Question

I was using the xfrontier function on stata, and I want to find the Psuedo $R^2$ of a model using log-likelihoods. Usually, you want a negative one, so you can subtract the ratio of full v intercept model, but I got a positive one from my output. Is there any way to derive an $R^2$ value from these numbers? I am really confused and could use some assistance.