C. Manipulating Historytime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputAs a human, she can erase history of its entirety. As a Bai Ze (Hakutaku), she can create history out of nothingness.—Perfect Memento in Strict SenseKeine has the ability to manipulate history. The history of Gensokyo is a string s of length 1 initially. To fix the chaos caused by Yukari, she needs to do the following operations n times, for the i-th time:  She chooses a non-empty substring t_{2i-1} of s. She replaces t_{2i-1} with a non-empty string, t_{2i}. Note that the lengths of strings t_{2i-1} and t_{2i} can be different.Note that if t_{2i-1} occurs more than once in s, exactly one of them will be replaced.For example, let s="marisa", t_{2i-1}="a", and t_{2i}="z". After the operation, s becomes "mzrisa" or "marisz".After n operations, Keine got the final string and an operation sequence t of length 2n. Just as Keine thinks she has finished, Yukari appears again and shuffles the order of t. Worse still, Keine forgets the initial history. Help Keine find the initial history of Gensokyo!Recall that a substring is a sequence of consecutive characters of the string. For example, for string "abc" its substrings are: "ab", "c", "bc" and some others. But the following strings are not its substring: "ac", "cba", "acb".HacksYou cannot make hacks in this problem.InputEach test contains multiple test cases. The first line contains a single integer T (1 \leq T \leq 10^3) — the number of test cases. The description of the test cases follows.The first line of each test case contains a single integer n (1 \le n < 10 ^ 5) — the number of operations.The next 2n lines contains one non-empty string t_{i} — the i-th string of the shuffled sequence t.The next line contains one non-empty string s — the final string.It is guaranteed that the total length of given strings (including t_i and s) over all test cases does not exceed 2 \cdot 10 ^ 5. All given strings consist of lowercase English letters only.It is guaranteed that the initial string exists. It can be shown that the initial string is unique.OutputFor each test case, print the initial string in one line.ExampleInput
2
2
a
ab
b
cd
acd
3
z
a
a
aa
yakumo
ran
yakumoran
Output
a
z
NoteTest case 1:Initially s is "a". In the first operation, Keine chooses "a", and replaces it with "ab". s becomes "ab". In the second operation, Keine chooses "b", and replaces it with "cd". s becomes "acd".So the final string is "acd", and t=["a", "ab", "b", "cd"] before being shuffled.Test case 2:Initially s is "z". In the first operation, Keine chooses "z", and replaces it with "aa". s becomes "aa". In the second operation, Keine chooses "a", and replaces it with "ran". s becomes "aran". In the third operation, Keine chooses "a", and replaces it with "yakumo". s becomes "yakumoran".So the final string is "yakumoran", and t=["z", "aa", "a", "ran", "a", "yakumo"] before being shuffled.
2
2
a
ab
b
cd
acd
3
z
a
a
aa
yakumo
ran
yakumoran

a z 
['constructive algorithms', 'greedy', 'strings', '*1700']