B"Let's call two strings a and b (both of length k ) a bit similar if they have the same character in some position, i. e. there exists at least one i in [1, k] such that a_i = b_i . You are given a binary string s of length n (a string of n characters 0 and/or 1) and an integer k . Let's denote the string s[i..j] as the substring of s starting from the i -th character and ending with the j -th character (that is, s[i..j] = s_i s_{i + 1} s_{i + 2} ... s_{j - 1} s_j ). Let's call a binary string t of length k beautiful if it is a bit similar to all substrings of s having length exactly k ; that is, it is a bit similar to s[1..k], s[2..k+1], ... , s[n-k+1..n] . Your goal is to find the lexicographically smallest string t that is beautiful, or report that no such string exists. String x is lexicographically less than string y if either x is a prefix of y (and x ne y ), or there exists such i ( 1 <= i <= min(|x|, |y|) ), that x_i < y_i , and for any j ( 1 <= j < i ) x_j = y_j . The first line contains one integer q ( 1 <= q <= 10000 ) -- the number of test cases. Each test case consists of two lines. The first line of each test case contains two integers n and k ( 1 <= k <= n <= 10^6 ). The second line contains the string s , consisting of n characters (each character is either 0 or 1). It is guaranteed that the sum of n over all test cases does not exceed 10^6 . For each test case, print the answer as follows: "...