B'Recently, Vika was studying her favorite internet resource - Wikipedia. On the expanses of Wikipedia, she read about an interesting mathematical operation bitwise XOR, denoted by oplus . Vika began to study the properties of this mysterious operation. To do this, she took an array a consisting of n non-negative integers and applied the following operation to all its elements at the same time: a_i = a_i oplus a_{(i+1) bmod n} . Here x bmod y denotes the remainder of dividing x by y . The elements of the array are numbered starting from 0 . Since it is not enough to perform the above actions once for a complete study, Vika repeats them until the array a becomes all zeros. Determine how many of the above actions it will take to make all elements of the array a zero. If this moment never comes, output -1 . The first line contains a single integer n ( 1 <= n <= 2^{20} ) - the length of the array a . It is guaranteed that n can be represented as 2^k for some integer k ( 0 <= k <= 20 ). The second line contains n integers a_0, a_1, a_2, ... , a_{n-1} ( 0 <= a_i <= 10^9 ) - the elements of the array a . Output a single number - the minimum number of actions required to make all elements of the array a zero, or -1 if the array a will never become zero. In the first example, after one operation, the array a will become equal to [3, 3, 3, 3] . After one more operation, it will become equal to [0, 0, 0, 0] . In the second example, the array a initially consists only of zeros. In the third example, after one operation, the array a will become equal to [0] . '...