Maximum K to Sort a Permutation

You are given an integer array perm of length n, where perm is a permutation of the numbers in the range [0, n - 1].
You may swap elements at indices i and j only if
perm[i] AND perm[j] == x,
where AND denotes the bitwise AND operation, and x is a non-negative integer.
Your task is to find the maximum value of x such that it is possible to sort the array perm in non-decreasing order using any number of such allowed swaps.
If the permutation is already sorted, return 0.