Return number of hits in field

Hi!

My mapping is:

PUT /test
{
    "mappings": {
        "properties": {
            "lufi": {
                "properties": {
                    "duma": {
                        "type": "keyword"
                    }
                }
            }
        }
    }
}

Insert some data:

POST /test/_doc/777
{
    "lufi": [
        {
            "duma": "aaa"
        },
        {
            "duma": "aaa bbb"
        },
        {
            "duma": "ccc"
        }
    ]
}

Search for documents which 'duma' fields contains 'aaa', and I'd like to return the number of hits in the 'duma' fields:

POST /test/_search
{
    "query": {
        "match": {
            "lufi.duma": "aaa"
        }
    },
    "script_fields": {
        "cnt": {
            "script": {
                "lang": "painless",
                "source": "doc['lufi.duma'].size()"
            }
        }
    }
}

The result is:

{
    "took": 1,
    "timed_out": false,
    "_shards": {
        "total": 1,
        "successful": 1,
        "skipped": 0,
        "failed": 0
    },
    "hits": {
        "total": {
            "value": 1,
            "relation": "eq"
        },
        "max_score": 0.39556286,
        "hits": [
            {
                "_index": "test",
                "_type": "_doc",
                "_id": "777",
                "_score": 0.39556286,
                "_source": [],
                "fields": {
                    "cnt": [
                        3
                    ]
                }
            }
        ]
    }
}

My problem is, the 'cnt' field contains 3, number of all 'duma' fields, but I need only the hits number, which is 2, because two duma fields ('aaa' and 'aaa bbb') values contains 'aaa', 'ccc' not. How can I solve this?

Thank you!