B'There is an array a consisting of non-negative integers. You can choose an integer x and denote b_i=a_i oplus x for all 1 <= i <= n , where oplus denotes the bitwise XOR operation. Is it possible to choose such a number x that the value of the expression b_1 oplus b_2 oplus ldots oplus b_n equals 0 ? It can be shown that if a valid number x exists, then there also exists x such that ( 0 <= x < 2^8 ). Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 1000 ). The description of the test cases follows. The first line of the test case contains one integer n ( 1 <= n <= 10^3 ) -- the length of the array a . The second line of the test case contains n integers -- array a ( 0 <= a_i < 2^8 ). It is guaranteed that the sum of n over all test cases does not exceed 10^3 . For each set test case, print the integer x ( 0 <= x < 2^8 ) if it exists, or -1 otherwise. In the first test case, after applying the operation with the number 6 the array b becomes [7, 4, 3] , 7 oplus 4 oplus 3 = 0 . There are other answers in the third test case, such as the number 0 . '...