Given a list of integers, return the nth smallest integer in the list. **Only distinct elements should be considered** when calculating the answer. `n` will always be positive (`n > 0`)

If the nth small integer doesn't exist, return `-1` (C++) / `None` (Python) / `nil` (Ruby) / `null` (JavaScript).

Notes:
* "indexing" starts from 1
* huge lists (of 1 million elements) will be tested

## Examples

```python
nth_smallest([1, 3, 4, 5], 7)        ==> None  # n is more than the size of the list
nth_smallest([4, 3, 4, 5], 4)        ==> None  # 4th smallest integer doesn't exist
nth_smallest([45, -10, 4, 5, 4], 4)  ==> 45    # 4th smallest integer is 45
```

If you get a timeout, just try to resubmit your solution. However, if you ***always*** get a timeout, review your code.

```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 = 'import random\n\ndef partition(vector, left, right, pivotIndex):\n    pivotValue = vector[pivotIndex]\n    vector[pivotIndex], vector[right] = vector[right], vector[pivotIndex]  # Move pivot to end\n    storeIndex = left\n    for i in range(left, right):\n        if vector[i] < pivotValue:\n            vector[storeIndex], vector[i] = vector[i], vector[storeIndex]\n            storeIndex += 1\n    vector[right], vector[storeIndex] = vector[storeIndex], vector[right]  # Move pivot to its final place\n    return storeIndex\n\ndef select(vector, left, right, k):\n    "Returns the k-th smallest, (k >= 0), element of vector within vector[left:right+1] inclusive."\n    if k < len(vector):\n        while True:\n            pivotIndex = random.randint(left, right)     # select pivotIndex between left and right\n            pivotNewIndex = partition(vector, left, right, pivotIndex)\n            pivotDist = pivotNewIndex - left\n            if pivotDist == k:\n                return vector[pivotNewIndex]\n            elif k < pivotDist:\n                right = pivotNewIndex - 1\n            else:\n                k -= pivotDist + 1\n                left = pivotNewIndex + 1\n\ndef nth_smallest(arr, n):\n    unique = list(set(arr))\n    return select(unique, 0, len(unique)-1, n-1)'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'nth_smallest'
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: 7688