Yousef has given you an array (a) of (2n) integers. Every integer (x \in 0, n - 1) appears exactly twice in the array. Your task is to find a subarray (a_l, a_{l + 1}, \dots, a_r) that is a palindrome(^{\text{∗}}) such that its (\operatorname{mex}(a_l, a_{l + 1}, \dots, a_r))(^{\text{†}}) is maximized. Output this maximum possible value. (^{\text{∗}})A palindrome is a string that reads the same backward as forward, for example, strings "z" , "aaa" , "aba" , "abccba" are palindromes, but strings "codeforces" , "reality" , "ab" are not. (^{\text{†}})The (\operatorname{mex}) (minimum excludant) of an array of integers is defined as the smallest non-negative integer which does not occur in the array. For example: The (\operatorname{mex}) of (2,2,1) is (0), because (0) does not belong to the array. The (\operatorname{mex}) of (3,1,0,1) is (2), because (0) and (1) belong to the array, but (2) does not. The (\operatorname{mex}) of (0,3,1,2) is (4), because (0), (1), (2) and (3) belong to the array, but (4) does not. The first line contains a single integer (t) ((1 \le t \le 10^4)) — the number of test cases. The first line of each test case contains a single integer (n) ((1 \le n \le 10^5)). The second line of each test case contains (2n) integers (a_1, a_2, \dots, a_{2n}) ((0 \le a_i \le n-1)). It is guaranteed that every integer in the range (0, n-1) appears exactly twice. It is guaranteed that the sum of (2n) over all test cases does not exceed (2 \cdot 10^5). For each test case, output a single integer — the maximum (\operatorname{mex}) of any palindromic subarray. In the first test case, the only optimal subarray to choose is (a1, 8 = 1, 2, 0, 3, 3, 0, 2, 1), which is palindromic and has a (\operatorname{mex}) of (4). In the second test case, one of the optimal subarrays to choos