Mongodb using last result as the next query input?

I have a mongodb document as below.  I want to return the documents with Maximum CurrentTicks, but since the tick was dynamically generated, I would need to return it to a variable LastTick, but when I try to retireve it in to the next query

First Query:          var LastTick = db.HKMachineStatus_v2.aggregate({$group: {_id : '' , Tick: {$max: "$CurrentTicks"}}})
Second Query:     db.HKMachineStatus_v2.find({"CurrentTicks" : LastTick})

it just return me "Fetched 0 record(s) in 5ms" But there is no result to return.

Then I only run the first Query it did return me the result as the image attached Result_outPut_1.jpg .

So my questions are
1. how to retrieve the Tick's value from LastTick
2. will my second Query success if I run in that way?
3. if not what will be better way to do it?  


below are the mongodb documents sample.

{
    "_id" : ObjectId("580e1f26fa9382133c202a04"),
    "ProcessTime" : "24472016-22:47:58",
    "HostName" : "APPServer",
    "IPAddress" : "192.168.0.1",
    "OS" : " Linux",
    "Status" : "Machine running",
    "CurrentTicks" : "636129460749210826"
},
{
    "_id" : ObjectId("580e1f26fa9382133c202a05"),
    "ProcessTime" : "24472016-22:47:58",
    "HostName" : "APPServer2",
    "IPAddress" : "192.168.0.2",
    "OS" : " Linux",
    "Status" : "Machine running",
    "CurrentTicks" : "636129460749210826"
},
{
    "_id" : ObjectId("580e21e1fa9382133c202d16"),
    "ProcessTime" : "24582016-22:58:57",
    "HostName" : "DC",
    "IPAddress" : "192.168.0.43",
    "OS" : " Windows",
    "Status" : "Machine running",
    "CurrentTicks" : "636129467352901129"
},
{
    "_id" : ObjectId("580e21e1fa9382133c202d17"),
    "ProcessTime" : "24582016-22:58:57",
    "HostName" : "DC2",
    "IPAddress" : "192.168.0.45",
    "OS" : " Windows",
    "Status" : "Machine running",
    "CurrentTicks" : "636129467352901129"
}

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Result_output_1.JPG