I need to know total count of tags in mongodb. For example in below documents there are total 5 tags.
My documents are like-
{ 
    "_id" : ObjectId("59c2102e2526c34768e405f5"), 
    "Name" : "Ashish", 
    "tags" : [
        "java", 
        "python", 
        "c"
    ]
},
{ 
    "_id" : ObjectId("62c2102e2526c34768e405l8"), 
    "Name" : "Binay", 
    "tags" : [
        "Dotnet", 
        "perl"
    ]
}
