when I search with key, I want to get the only value from the mongodb documents

Question

I need a MongoDB query to get the only value from the document. I have the following two documents. I want to get the only value of service key from the second document.

{
    "develop-48" : [ 
        {
            "analytics" : "f58b6fc81b",
            "service" : "3e449ce020e2",
            "cdm" : "03e9e4f9423fd"
        }
    ]
}

and

{
    "develop-12" : [ 
        {
            "analytics" : "f58b6fc54b",
            "service" : "3e449ce020d3",
            "cdm" : "03e9e4f9423fd"
        }
    ]
}

The query that I have tried is db.den.find({},{"develop-12.service":1, "_id": 0})

and the output that I am getting is { } { "develop-12" : [ { "service" : "3e449ce020d3" } ] }

The expected output is 3e449ce020d3 If it is not possible, suggest me the best possible way to achieve this