You wrote all your unit test names in camelCase.
But some of your colleagues have troubles reading these long test names.
So you make a compromise to switch to underscore separation.

To make these changes fast you wrote a class to translate a camelCase name
into an underscore separated name.

Implement the ToUnderscore() method.

Example:

`"ThisIsAUnitTest" => "This_Is_A_Unit_Test"`


**But of course there are always special cases...**

You also have some calculation tests. Make sure the results don't get split by underscores.
So only add an underscore in front of the first number.

Also Some people already used underscore names in their tests. You don't want to change them.
But if they are not split correct you should adjust them.

Some of your colleagues mark their tests with a leading and trailing underscore.
Don't remove this.

And of course you should handle empty strings to avoid unnecessary errors. Just return an empty string then.

Example:

`"Calculate15Plus5Equals20" => "Calculate_15_Plus_5_Equals_20"`

`"This_Is_Already_Split_Correct" => "This_Is_Already_Split_Correct"`

`"ThisIs_Not_SplitCorrect" => "This_Is_Not_Split_Correct"`

`"_UnderscoreMarked_Test_Name_" => _Underscore_Marked_Test_Name_"`

```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 toUnderScore(name):\n    \n    list_of_chars = []\n    previous_char = None\n\n    for char in name:\n\n        if previous_char is not None and char != "_" and previous_char != "_":\n\n            if char.isupper() or char.isdigit() and not previous_char.isdigit():\n                list_of_chars.append("_")\n            \n        list_of_chars.append(char)\n        previous_char = char\n\n    return "".join(list_of_chars)'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'toUnderScore'
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: 5626