Watcher that outputs the total number of snapshots in a repository

How do I get the total number of snapshots from a repository with this input? I've tried ctx.payload.hits and ctx.payload.hits.value but the value is blank. Any help would be greatly appreciated.

  "input" : {
    "http" : {
      "request" : {
        "host" : "localhost",
        "port" : 9200,
        "path" : "_snapshot/<repo>/_all"
      }
    }
  }