How to remove square brackets of number in json array using json data extractor

My json response is

{
  "message": "Lead created successfully",
  "id": "[667]",
  "input_data": null,
  "result": [],
  "statusCode": 200
}

and I need only 667 to pass to an url as path param. I'm using $.id[0] using json data extractor , but getting response as [667] instead of 667, please help.