You are given $n$ strings $a_1, a_2, \ldots, a_n$: all of them have the same length $m$. The strings consist of lowercase English letters.

Find any string $s$ of length $m$ such that each of the given $n$ strings differs from $s$ in at most one position. Formally, for each given string $a_i$, there is no more than one position $j$ such that $a_i[j] \ne s[j]$.

Note that the desired string $s$ may be equal to one of the given strings $a_i$, or it may differ from all the given strings.

For example, if you have the strings abac and zbab, then the answer to the problem might be the string abab, which differs from the first only by the last character, and from the second only by the first.


-----Input-----

The first line contains an integer $t$ ($1 \le t \le 100$) — the number of test cases. Then $t$ test cases follow.

Each test case starts with a line containing two positive integers $n$ ($1 \le n \le 10$) and $m$ ($1 \le m \le 10$) — the number of strings and their length.

Then follow $n$ strings $a_i$, one per line. Each of them has length $m$ and consists of lowercase English letters.


-----Output-----

Print $t$ answers to the test cases. Each answer (if it exists) is a string of length $m$ consisting of lowercase English letters. If there are several answers, print any of them. If the answer does not exist, print "-1" ("minus one", without quotes).


-----Example-----
Input
5
2 4
abac
zbab
2 4
aaaa
bbbb
3 3
baa
aaa
aab
2 2
ab
bb
3 1
a
b
c

Output
abab
-1
aaa
ab
z


-----Note-----

The first test case was explained in the statement.

In the second test case, the answer does not exist.

```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 = 'def check(a, b):\n  dif = 0\n  for i in range(len(a)):\n    if a[i] != b[i]:\n      dif += 1\n      if dif == 2:\n        return False\n  return True\n\nfor _ in range(int(input())):\n  n, m = map(int, input().split())\n  data = []\n  for i in range(n):\n    data.append(input())\n\n  result = False\n  for i in range(m):\n    for j in range(0, 26):\n      now = data[0][:i] + chr(ord(\'a\') + j) + data[0][i + 1:]\n      temp = True\n      for k in data[1:]:\n        if not check(now, k):\n          temp = False\n      if temp:\n        print(now)\n        result = True\n        break\n    if result:\n      break\n  \n  if not result:\n    print("-1")'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

```

Measured memory_bytes: 13447