C. Phase Shifttime limit per test3 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputThere was a string s which was supposed to be encrypted. For this reason, all 26 lowercase English letters were arranged in a circle in some order, afterwards, each letter in s was replaced with the one that follows in clockwise order, in that way the string t was obtained. You are given a string t. Determine the lexicographically smallest string s that could be a prototype of the given string t.A string a is lexicographically smaller than a string b of the same length if and only if:   in the first position where a and b differ, the string a has a letter, that appears earlier in the alphabet than the corresponding letter in b.  InputThe first line of the input contains a single integer t (1 \le t \le 3 \cdot 10^4) — the number of test cases. The description of test cases follows.The first line of each test case contains one integer n (1 \le n \le 10^5) — the length of the string t.The next line contains the string t of the length n, containing lowercase English letters.It is guaranteed that the sum of n over all test cases doesn't exceed 2 \cdot 10^5.OutputFor each test case, output a single line containing the lexicographically smallest string s which could be a prototype of t.ExampleInput
51a2ba10codeforces26abcdefghijklmnopqrstuvwxyz26abcdefghijklmnopqrstuvwxzyOutput
b
ac
abcdebfadg
bcdefghijklmnopqrstuvwxyza
bcdefghijklmnopqrstuvwxyaz
NoteIn the first test case, we couldn't have the string "a", since the letter a would transit to itself. Lexicographically the second string "b" is suitable as an answer.In the second test case, the string "aa" is not suitable, since a would transit to itself. "ab" is not suitable, since the circle would be closed with 2 letters, but it must contain all 26. The next string "ac" is suitable.Below you can see the schemes for the first three test cases. The non-involved letters are skipped, they can be arbitrary placed in the gaps.  
51a2ba10codeforces26abcdefghijklmnopqrstuvwxyz26abcdefghijklmnopqrstuvwxzy
b ac abcdebfadg bcdefghijklmnopqrstuvwxyza bcdefghijklmnopqrstuvwxyaz 
['dfs and similar', 'dsu', 'graphs', 'greedy', 'implementation', 'strings', '*1400']