How is the final score of a LambdaMart model calculated?

[meg261995]

So I am using Elasticsearch LTR plugin for ranking purposes and I have trained an sltr model "my-model" with 4 features.. The below is the explanation of how the score is calculated got by the "explain" parameter of the query. I understood the inner details but having a trouble in understanding how the final score 2.777. Usually the description mentions if the score is either a "product of ","sum of", "min or max". Here I am not able to understand. Can anyone please help me with this:

{ "value": 2.777724,
"description": " LtrModel: LambdaMART using features:",
"details": [ { "value": 12.079079, "description": "Feature 0('feat1')", "details": [ ..... ] },
{ "value": 17.195917, "description": "Feature 1(feat2):", "details": [ ... ] },
{ "value": 0, "description": "Feature 2(feat3):", "details": [ .... ] },
{ "value": 0.8042648, "description": "Feature 3(feat4):", "details": [ .... ] } }