Description: You are given an array $$$a$$$ consisting of $$$n$$$ integers. The array is sorted if $$$a_1 \le a_2 \le \dots \le a_n$$$. You want to make the array $$$a$$$ sorted by applying the following operation exactly once: - choose an integer $$$x$$$, then for every $$$i \in [1, n]$$$, replace $$$a_i$$$ by $$$|a_i - x|$$$. Find any value of $$$x$$$ that will make the array sorted, or report that there is no such value. Input Format: The first line contains one integer $$$t$$$ ($$$1 \le t \le 2 \cdot 10^4$$$) — the number of test cases. Each test case consists of two lines. The first line contains one integer $$$n$$$ ($$$2 \le n \le 2 \cdot 10^5$$$). The second line contains $$$n$$$ integers $$$a_1, a_2, \dots, a_n$$$ ($$$1 \le a_i \le 10^8$$$). Additional constraint on the input: the sum of $$$n$$$ over all test cases does not exceed $$$2 \cdot 10^5$$$. Output Format: For each test case, print any integer $$$x$$$ ($$$0 \le x \le 10^9$$$) 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. Note: 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 $$$[32, 37, 38, 39, 40, 41]$$$.