B'You are given a positive integer x . You can apply the following operation to the number: remove one occurrence of any digit in such a way that the resulting number does not contain any leading zeroes and is still a positive integer. For example, 10142 can be converted to 1142 , 1042 , 1012 or 1014 (note that 0142 is not a valid outcome); 10 can be converted to 1 (but not to 0 since it is not positive). Your task is to find the minimum positive integer that you can obtain from x if you can apply the aforementioned operation exactly k times. The first line contains a single integer t ( 1 <= t <= 10^5 ) -- the number of test cases. The first line of each test case contains a single integer x ( 1 <= x < 10^{500000} ). The second line contains a single integer k ( 0 <= k < |x| ), where |x| is the length of the number x . The sum of |x| over all test cases does not exceed 5 cdot 10^5 . For each test case, print one integer -- the minimum positive number that you can obtain from x if you can apply the operation exactly k times. '...