B'You are given an array a_1, a_2, ... , a_n of distinct positive integers. You have to do the following operation exactly once: Find a value of k such that 1 <= q k <= q 10^{18} and the array a_1, a_2, ... , a_n contains exactly 2 distinct values at the end of the operation. It can be shown that, under the constraints of the problem, at least one such k always exists. If there are multiple solutions, you can print any of them. ^ dagger a text{ mod } b denotes the remainder after dividing a by b . For example: Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 500 ). The description of the test cases follows. The first line of each test case contains a single integer n ( 2 <= n <= 100 ) -- the length of the array a . The second line of each test case contains n integers a_1, a_2, ldots, a_n ( 1 <= a_i <= 10^{17} ) -- the initial state of the array. It is guaranteed that all the a_i are distinct. Note that there are no constraints on the sum of n over all test cases. For each test case, output a single integer: a value of k ( 1 <= q k <= q 10^{18} ) such that the array a_1, a_2, ... , a_n contains exactly 2 distinct values at the end of the operation. In the first test case, you can choose k = 7 . The array becomes [8 text{ mod } 7, 15 text{ mod } 7, 22 text{ mod } 7, 30 text{ mod } 7] = [1, 1, 1, 2] , which contains exactly 2 distinct values ( {1, 2 } ). In the second test case, you can choose k = 30 . The array becomes [0, 0, 8, 0, 8] , which contains exactly 2 distinct values ( {0, 8 } ). Note that choosing k = 10 would also be a valid solution. In the last test case, you can choose k = 10^{18} . The array becomes [2, 1] , which contains exactly 2 distinct values ( {1, 2 } ). Note that '...