B'You are given an array a consisting of n integers. The array is sorted if a_1 <= a_2 <= ... <= a_n . You want to make the array a sorted by applying the following operation exactly once: Find any value of x that will make the array sorted, or report that there is no such value. The first line contains one integer t ( 1 <= t <= 2 cdot 10^4 ) -- the number of test cases. Each test case consists of two lines. The first line contains one integer n ( 2 <= n <= 2 cdot 10^5 ). The second line contains n integers a_1, a_2, ... , a_n ( 1 <= a_i <= 10^8 ). Additional constraint on the input: the sum of n over all test cases does not exceed 2 cdot 10^5 . For each test case, print any integer x ( 0 <= x <= 10^9 ) that makes the array sorted. It can be shown that if such an integer x exists, there is at least one such integer between 0 and 10^9 . If there is no such integer, then print -1 . If there are multiple suitable values of x , print any of them. In the first test case, after using x = 4 , the array becomes [1, 1, 1, 1, 1] . In the third test case, after using x = 0 , the array becomes [1, 2, 3, 4, 5, 6, 7, 8] . In the fourth test case, after using x = 42 , the array becomes [32, 37, 38, 39, 40, 41] . '...