Increment field of Elasticsearch from logstash

Elastic Stack Elasticsearch
1

I have one field
index = in
type = mytype
field =
...
...
count
...
...

i just want to write a script which will update my count field by 1 in ES leaving rest as it was from logstash,

so my logstash *.conf file looks like
so input to logstash is

id=ET12 (script should increment count field in elasticsearch by one of this id)

  input { 
	http {
    ...
  }
}

output { 
  stdout { codec => json }
}

what should go inside output of logstash to achieve what i want?
kindly help
thanks