How to get the Value in the element of JSON by JSONPath?

This is my JSON data

{
    "code": 0,
    "message": "success",
    "data": {
        "logFrom": "{\"date_as_long\": 1411455611975}"
    }
}

The logFrom object is still a JSON.

In this case, how can I use JSONPath expression to locate date_as_long?