Get buckets count before bucket_sort

I have a question about elasticsearch aggregations.How to get bucket count before bucket_sort paged, code:

 "aggs": {
    ...
      "fitler": {
        "bucket_selector": {
          "buckets_path": {
            "orderCount": "_count"
          },
          "script": "params.orderCount == 1",
          "gap_policy": "skip"
        }
      },
      "r_bucket_sort":{
          "bucket_sort": {
              "sort": [{"user_sort":{"order":"desc" }}],
              "from": 1,
              "size": 5
          }
        }
    }
  },
  "total":{ 
    "cardinality": {
      "field":"id.keyword"
  }
}  

the total cant return bucket count.