B'Phoenix has a string s consisting of lowercase Latin letters. He wants to distribute all the letters of his string into k non-empty strings a_1, a_2, ... , a_k such that every letter of s goes to exactly one of the strings a_i . The strings a_i do not need to be substrings of s . Phoenix can distribute letters of s and rearrange the letters within each string a_i however he wants. For example, if s = baba and k=2 , Phoenix may distribute the letters of his string in many ways, such as: But these ways are invalid: Phoenix wants to distribute the letters of his string s into k strings a_1, a_2, ... , a_k to minimize the lexicographically maximum string among them, i. e. minimize max(a_1, a_2, ... , a_k) . Help him find the optimal distribution and print the minimal possible value of max(a_1, a_2, ... , a_k) . String x is lexicographically less than string y if either x is a prefix of y and x ne y , or there exists an index i ( 1 <= i <= min(|x|, |y|)) such that x_i < y_i and for every j (1 <= j < i) x_j = y_j . Here |x| denotes the length of the string x . The input consists of multiple test cases. The first line contains an integer t ( 1 <= t <= 1000 ) -- the number of test cases. Each test case consists of two lines. The first line of each test case consists of two integers n and k ( 1 <= k <= n <= 10^5 ) -- the length of string s and the number of non-empty strings, into which Phoenix wants to distribute letters of s , respectively. The second line of each test case contains a string s of length n consisting only of lowercase Latin letters. It is guaranteed that the sum of n over all test cases is <= 10^5 . Print t answers -- one per test case. The i -th answer should be the minimal possible va'...