B'Note that the only difference between String Transformation 1 and String Transformation 2 is in the move Koa does. In this version the letter y Koa selects must be strictly greater alphabetically than x (read statement for better understanding). You can make hacks in these problems independently. Koa the Koala has two strings A and B of the same length n ( |A|=|B|=n ) consisting of the first 20 lowercase English alphabet letters (ie. from a to t). In one move Koa: Note that you can only modify letters in string A . Koa wants to know the smallest number of moves she has to do to make strings equal to each other ( A = B ) or to determine that there is no way to make them equal. Help her! Each test contains multiple test cases. The first line contains t ( 1 <= t <= 10 ) -- the number of test cases. Description of the test cases follows. The first line of each test case contains one integer n ( 1 <= n <= 10^5 ) -- the length of strings A and B . The second line of each test case contains string A ( |A|=n ). The third line of each test case contains string B ( |B|=n ). Both strings consists of the first 20 lowercase English alphabet letters (ie. from a to t). It is guaranteed that the sum of n over all test cases does not exceed 10^5 . For each test case: Print on a single line the smallest number of moves she has to do to make strings equal to each other ( A = B ) or -1 if there is no way to make them equal. '...