Write a function that takes a positive integer and returns the next smaller positive integer containing the same digits.

For example:

```python
next_smaller(21) == 12
next_smaller(531) == 513
next_smaller(2071) == 2017
```

Return -1 (for `Haskell`: return `Nothing`, for `Rust`: return `None`), when there is no smaller number that contains the same digits. Also return -1 when the next smaller number with the same digits would require the leading digit to be zero.

```python 
next_smaller(9) == -1
next_smaller(135) == -1
next_smaller(1027) == -1  # 0721 is out since we don't write numbers with leading zeros
```
```ruby 
next_smaller(9) == -1
next_smaller(135) == -1
next_smaller(1027) == -1  # 0721 is out since we don't write numbers with leading zeros
```

 * some tests will include very large numbers.
 * test data only employs positive integers.

*The function you write for this challenge is the inverse of this kata: "[Next bigger number with the same digits](http://www.codewars.com/kata/next-bigger-number-with-the-same-digits)."*

```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 next_smaller(n):\n    \n    ## Create a list of each digit in n\n    numbers = [int(i) for i in str(n)]\n\n    ## Loop over each digit in the numbers list, from right to left\n    for i in range(len(numbers) - 1, 0, -1):\n    \n        ## If a number is less than the number to its left, split into 2 lists\n        if numbers[i] < numbers[i -1]:\n            rearrange_list = numbers[i - 1:]  ## numbers on the right of i -1\n            original_list = numbers[:i - 1]   ## numbers on the left of i -1\n            less_than_values = []             ## will contain possible substitutions for i -1\n            \n            ## Loop over the rearrange_list\n            for i in rearrange_list:\n            \n                ## if the number is smaller than i, append it to less_than_values\n                if i < rearrange_list[0]:\n                    less_than_values.append(i)\n    \n            ## Add the max value from less_than_values to the end of the original_list, \n            ## then add the rest of the sorted values from rearrange_list to the original_list\n            original_list.append(max(less_than_values))\n            rearrange_list.remove(max(less_than_values))\n            original_list += sorted(rearrange_list, reverse=True)\n            \n            ## Join the list together to get the output\n            output = int(''.join([str(num) for num in original_list]))\n\n            ## If the output starts with 0, return -1. Otherwise, return the ouput.\n            if len(str(output)) < len(str(n)):\n                return -1\n            else:\n                return output\n    \n    ## Return -1 if n is None, or if there are no smaller numbers\n    return -1            \n"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'next_smaller'
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: 6462