# Calculate probabilities from xgb dump for multi:softprob objective - formula?

On dumping the xgboost (with objective of multi:softprob) for binary classification, I see booster dumps as: class0_booster0, class1_booster0, class0_booster1, class1_booster1, etc. I have noted down all the leaf values for class 0. How do I, then, calculate the probability for class 0? (I've tried 1/1+exp(-S), where S is the sum of all leaves, but had no luck.)