Define a function that takes in two non-negative integers `$a$` and `$b$` and returns the last decimal digit of `$a^b$`. Note that `$a$` and `$b$` may be very large!

For example, the last decimal digit of `$9^7$` is `$9$`, since `$9^7 = 4782969$`.  The last decimal digit of `$({2^{200}})^{2^{300}}$`, which has over `$10^{92}$` decimal digits, is `$6$`.  Also, please take `$0^0$` to be `$1$`.

You may assume that the input will always be valid.

## Examples

```python
last_digit(4, 1)                # returns 4
last_digit(4, 2)                # returns 6
last_digit(9, 7)                # returns 9
last_digit(10, 10 ** 10)        # returns 0
last_digit(2 ** 200, 2 ** 300)  # returns 6
```

___

## Remarks

### JavaScript, C++, R, PureScript

Since these languages don't have native arbitrarily large integers, your arguments are going to be strings representing non-negative integers instead.

```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 = 'digits = {\n    0:[0,0,0,0],   \n    1:[1,1,1,1],   \n    2:[2,4,8,6],   \n    3:[3,9,7,1],   \n    4:[4,6,4,6],   \n    5:[5,5,5,5],   \n    6:[6,6,6,6],   \n    7:[7,9,3,1],   \n    8:[8,4,2,6], \n    9:[9,1,9,1]\n}\ndef last_digit(n1, n2):\n    return digits[n1%10][(n2-1)%4] if n2 else 1'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'last_digit'
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: 5326