I'm trying to decode JSON format

What I am sending is:

```
{
"id": 123,
"name": "John",
“surname”: “Smith”,
“department”: 3
}

```

I am sending POST with data via Postman, in the picture.  

So, this is the data I want to decode:

```
"data_serever_received": "{ \"id\": 123, \"name\": \"john\", “surname”: “Smith”, “department”: 3 }"

```

![enter image description here](https://i.stack.imgur.com/UEiZC.png)

I tried

```
$this->input->data["id"]

```

but it is not working.

How can I get the id, name, surname and etc. values?