B'Serval has two n -bit binary integer numbers a and b . He wants to share those numbers with Toxel. Since Toxel likes the number b more, Serval decides to change a into b by some (possibly zero) operations. In an operation, Serval can choose any positive integer k between 1 and n , and change a into one of the following number: In other words, the operation moves every bit of a left or right by k positions, where the overflowed bits are removed, and the missing bits are padded with 0 . The bitwise XOR of the shift result and the original a is assigned back to a . Serval does not have much time. He wants to perform no more than n operations to change a into b . Please help him to find out an operation sequence, or determine that it is impossible to change a into b in at most n operations. You do not need to minimize the number of operations. In this problem, x oplus y denotes the bitwise XOR operation of x and y . a ll k and a gg k denote the logical left shift and logical right shift. Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 2 cdot10^{3} ). The description of the test cases follows. The first line of each test case contains a single integer n ( 1 <= n <= 2 cdot10^{3} ) -- the number of bits in numbers a and b . The second and the third line of each test case contain a binary string of length n , representing a and b , respectively. The strings contain only characters 0 and 1. It is guaranteed that the sum of n over all test cases does not exceed 2 cdot10^{3} . For each test case, if it is impossible to change a into b in at most n operations, print a single integer -1 . Otherwise, in the first line, print the number of operations m ( 0 <= m <= n ). If m>0 '...