The image shows how we can obtain the Harmonic Conjugated Point of three aligned points A, B, C.

- We choose any point L, that is not in the line with A, B and C. We form the triangle ABL

- Then we draw a line from point C that intersects the sides of this triangle at points M and N respectively.

- We draw the diagonals of the quadrilateral ABNM; they are AN and BM and they intersect at point K

- We unit, with a line L and K, and this line intersects the line of points A, B and C at point D

The point D is named the Conjugated Harmonic Point of the points A, B, C.
You can get more knowledge related with this point at: (https://en.wikipedia.org/wiki/Projective_harmonic_conjugate)

If we apply the theorems of Ceva (https://en.wikipedia.org/wiki/Ceva%27s_theorem)
and Menelaus (https://en.wikipedia.org/wiki/Menelaus%27_theorem) we will have this formula:



AC, in the above formula is the length of the segment of points A to C in this direction and its value is:

```AC = xA - xC```

Transform the above formula using the coordinates ```xA, xB, xC and xD```

The task is to create a function ```harmon_pointTrip()```, that receives three arguments, the coordinates of points xA, xB and xC, with values such that : ```xA < xB < xC```, this function should output the coordinates of point D for each given triplet, such that

`xA < xD < xB < xC`, or to be clearer

let's see some cases:
```python
harmon_pointTrip(xA, xB, xC) ------> xD # the result should be expressed up to four decimals (rounded result)
harmon_pointTrip(2, 10, 20) -----> 7.1429 # (2 < 7.1429 < 10 < 20, satisfies the constraint)
harmon_pointTrip(3, 9, 18) -----> 6.75
```


Enjoy it and happy coding!!

```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 harmon_pointTrip(a, b, c):\n    return round((2.0*a*b - b*c - a*c) / (a + b - 2*c), 4)'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'harmon_pointTrip'
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: 5466