You are given a permutation (a) and (b) of length (n)(^{\text{∗}}). You can perform the following operation at most (n) times: Choose two indices (i) and (j) ((1 \le i, j \le n), (i \ne j)), swap (a_i) with (a_j), swap (b_i) with (b_j). Determine whether (a) and (b) can be reverses of each other after operations. In other words, for each (i = 1, 2, \ldots, n), (a_i = b_{n + 1 - i}). If it is possible, output any valid sequence of operations. Otherwise, output (-1). (^{\text{∗}})A permutation of length (n) is an array consisting of (n) distinct integers from (1) to (n) in arbitrary order. For example, (2,3,1,5,4) is a permutation, but (1,2,2) is not a permutation ((2) appears twice in the array), and (1,3,4) is also not a permutation ((n=3) but there is (4) in the array). Each test contains multiple test cases. The first line contains the number of test cases (t) ((1 \le t \le 10^4)). The description of the test cases follows. The first line of each test case contains a single integer (n) ((2 \le n \le 2 \cdot 10^5)) — the length of the permutations. The second line contains (n) integers (a_1, a_2, \ldots, a_n) ((1 \le a_i \le n)). The third line contains (n) integers (b_1, b_2, \ldots, b_n) ((1 \le b_i \le n)). It is guaranteed that (a) and (b) are permutations of length (n). It is guaranteed that the sum of (n) over all test cases does not exceed (2\cdot 10^5). For each test case, if it is impossible, output (-1) in the only line. Otherwise, output a single integer (m) ((0 \le m \le n)) — the number of operations in the first line. In the following (m) lines, output two integers — the indices (i) and (j) ((1 \le i, j \le n), (i \ne j)) in each operation in order. If there are multiple solutions, print any of them. In the second test case, $$$b$$