You have a set of four (4) balls labeled with different numbers: ball_1 (1), ball_2 (2), ball_3 (3) and ball(4) and we have 3 equal boxes for distribute them. The possible combinations of the balls, without having empty boxes, are:

```
 (1)            (2)        (3)(4)     
______        ______       _______ 
    
```

```
 (1)           (2)(4)        (3)
______         ______      ______
  
```

```
(1)(4)           (2)         (3)
______          ______      ______

```

```
  (1)           (2)(3)       (4)
_______         _______     ______

```

```
(1)(3)            (2)        (4)
_______         _______     ______
```

```
(1)(2)            (3)        (4)
_______         _______     ______
```
We have a total of **6** combinations.

Think how many combinations you will have with two boxes instead of three. You will obtain **7** combinations.

Obviously, the four balls in only box will give only one possible combination (the four balls in the unique box). Another particular case is the four balls in four boxes having again one possible combination(Each box having one ball).

What will be the reasonable result for a set of n elements with no boxes?

Think to create a function that may calculate the amount of these combinations of a set of ```n``` elements in ```k``` boxes.

You do no not have to check the inputs type that will be always valid integers.

The code should detect the cases when ```k > n```, returning "It cannot be possible!". 

Features of the random tests:
```
1 <= k <= n <= 800
```
Ruby version will be published soon.

```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 = "# Stirling numbers of second kind\n# http://mathworld.wolfram.com/StirlingNumberoftheSecondKind.html\n# S(n,k)=1/(k!)sum_(i=0)^k(-1)^i(k; i)(k-i)^n\nfrom math import factorial as fact\n\ndef combs_non_empty_boxes(n,k):\n    if k<0 or k>n: return 'It cannot be possible!'\n    return sum([1,-1][i%2]*(k-i)**n*fact(k)//(fact(k-i)*fact(i)) for i in range(k+1))//fact(k)"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'combs_non_empty_boxes'
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: 5880