We need you to implement a method of receiving commands over a network, processing the information and responding.

Our device will send a single packet to you containing data and an instruction which you must perform before returning your reply.

To keep things simple, we will be passing a single "packet" as a string. 
Each "byte" contained in the packet is represented by 4 chars.



One packet is structured as below:
```
Header  Instruction   Data1    Data2   Footer
------   ------       ------   ------  ------
 H1H1     0F12         0012     0008    F4F4
------   ------       ------   ------  ------

The string received in this case would be - "H1H10F1200120008F4F4"

Instruction: The calculation you should perform, always one of the below.
            0F12 = Addition
            B7A2 = Subtraction
            C3D9 = Multiplication
            FFFF = This instruction code should be used to identify your return value.
``` 
- The Header and Footer are unique identifiers which you must use to form your reply.

- Data1 and Data2 are the decimal representation of the data you should apply your instruction to. _i.e 0109 = 109._

- Your response must include the received header/footer, a "FFFF" instruction code, and the result of your calculation stored in Data1.

- Data2 should be zero'd out to "0000".


```
To give a complete example:

If you receive message "H1H10F1200120008F4F4".
The correct response would be "H1H1FFFF00200000F4F4"

```
In the event that your calculation produces a negative result, the value returned should be "0000", similarily if the value is above 9999 you should return "9999".


Goodluck, I look forward to reading your creative solutions!

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = "def communication_module(packet):\n    header, footer = packet[:4], packet[-4:]\n    instr, rvalue = packet[4:8], 'FFFF'\n    data1, data2 = packet[8:12], packet[12:16]\n    \n    if instr == '0F12':\n        calc = int(data1) + int(data2)\n    elif instr == 'B7A2':\n        calc = int(data1) - int(data2)\n    elif instr == 'C3D9':\n        calc = int(data1) * int(data2)\n        \n    if calc > 9999:\n        calc = 9999\n    elif calc < 0:\n        calc = 0\n        \n    rstring = f'{header}{rvalue}{calc:04d}0000{footer}'\n    \n    return rstring"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'communication_module'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 5723