Iroha has a sequence of N strings S_1, S_2, ..., S_N. The length of each string is L.
She will concatenate all of the strings in some order, to produce a long string.
Among all strings that she can produce in this way, find the lexicographically smallest one.
Here, a string s=s_1s_2s_3...s_n is lexicographically smaller than another string t=t_1t_2t_3...t_m if and only if one of the following holds:

 - There exists an index i(1≦i≦min(n,m)), such that s_j = t_j for all indices j(1≦j<i), and s_i<t_i.
 - s_i = t_i for all integers i(1≦i≦min(n,m)), and n<m.

-----Constraints-----
 - 1 ≦ N, L ≦ 100
 - For each i, the length of S_i equals L.
 - For each i, S_i consists of lowercase letters.

-----Input-----
The input is given from Standard Input in the following format:
N L
S_1
S_2
:
S_N

-----Output-----
Print the lexicographically smallest string that Iroha can produce.

-----Sample Input-----
3 3
dxx
axx
cxx

-----Sample Output-----
axxcxxdxx

The following order should be used: axx, cxx, dxx.

```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

ns = {"__name__": "__main__"}
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = "#from statistics import median\n#import collections\n#aa = collections.Counter(a) # list to list || .most_common(2)で最大の2個とりだせるお a[0][0]\nfrom math import gcd\nfrom itertools import combinations,permutations,accumulate, product # (string,3) 3回\n#from collections import deque\nfrom collections import deque,defaultdict,Counter\nimport decimal\nimport re\nimport math\nimport bisect\nimport heapq\n#\n#\n#\n# pythonで無理なときは、pypyでやると正解するかも！！\n#\n#\n# my_round_int = lambda x:np.round((x*2 + 1)//2)\n# 四捨五入g\n#\n# インデックス系\n# int min_y = max(0, i - 2), max_y = min(h - 1, i + 2);\n# int min_x = max(0, j - 2), max_x = min(w - 1, j + 2);\n#\n#\nimport sys\nsys.setrecursionlimit(10000000)\nmod = 10**9 + 7\n#mod = 9982443453\n#mod = 998244353\nINF = float('inf')\nfrom sys import stdin\nreadline = stdin.readline\ndef readInts():\n  return list(map(int,readline().split()))\ndef readTuples():\n    return tuple(map(int,readline().split()))\ndef I():\n    return int(readline())\nn,l = readInts()\nlis = [input() for _ in range(n)]\nlis = sorted(lis)\nprint((''.join(lis)))\n"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

```

Measured memory_bytes: 14479