You have been given a set of N strings S1, S2, .... SN. Consider any non-empty string S (S need not belong to the given set of N strings). Suppose S occurs (as a substring) in K out of the N given strings in the set. Your job is to choose S such that the value of K is maximized. If there are many such strings, choose the one with the least length. If there are many such strings with the least length, choose the lexicographically smallest of them all.

Input:

The first line consists of T the number of test cases.
The first line in each test case consists of N, the number of words in the given set. Each of the next N lines contains a single word consisting of lowercase English alphabets (a-z) only.

Output:

Print the answer to each test case on a new line, the answer to each test case being a single string S as described in the problem above.

Constraints :

1 ≤ T ≤ 5

1 ≤ N ≤ 100

1 ≤ |Si| ≤ 100, |Si| denotes the length of the input words.

Author : Himanshu

Tester : Shreyans

(By IIT Kgp HackerEarth Programming Club)

SAMPLE INPUT
1
1
shades

SAMPLE OUTPUT
a
'''
# Read input from stdin and provide input before running code

name = raw_input('What is your name?\n')
print 'Hi, %s.' % name
'''
tc =raw_input('')
for i in range(int(tc)):
	num =raw_input('')
	words = []
	for j in range(int(num)):

		d=raw_input('')
		words.append(d)
	count = []

	for i in range(26):
		count.append(0)

	for k in words:
		a='a'
		for i in range(26):
			if a in k:
				count[i] = count[i] + 1
			a=chr(ord(a) + 1)
	print chr(count.index(max(count))+97)