B'You are given an integer n and a string s consisting of 2^n lowercase letters of the English alphabet. The characters of the string s are s_0s_1s_2 cdots s_{2^n-1} . A string t of length 2^n (whose characters are denoted by t_0t_1t_2 cdots t_{2^n-1} ) is a xoration of s if there exists an integer j ( 0 <= j <= q 2^n-1 ) such that, for each 0 <= q i <= q 2^n-1 , t_i = s_{i oplus j} (where oplus denotes the operation bitwise XOR). Find the lexicographically minimal xoration of s . A string a is lexicographically smaller than a string b if and only if one of the following holds: The first line contains a single integer n ( 1 <= n <= 18 ). The second line contains a string s consisting of 2^n lowercase letters of the English alphabet. Print a single line containing the lexicographically minimal xoration of s . In the first test, the lexicographically minimal xoration t of s = "acba" is "abca". It 's a xoration because, for j = 3 , In the second test, the minimal string xoration corresponds to choosing j = 4 in the definition of xoration. In the third test, the minimal string xoration corresponds to choosing j = 11 in the definition of xoration. In the fourth test, the minimal string xoration corresponds to choosing j = 10 in the definition of xoration. In the fifth test, the minimal string xoration corresponds to choosing either j = 0 or j = 1 in the definition of xoration. '...