import string
import sys
from itertools import accumulate
from typing import List, Tuple


def int1(x: str, /): return int(x) - 1


def input(): return sys.stdin.readline().rstrip('\n')


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()), sep='; ', file=sys.stderr)


def main():
    n = int(input())
    *a, = map(int, input().split())
    d = [0 for _ in range(1 << n)]
    for i in range(1 << n):
        for j in range(n):
            for k in range(j):
                if (i & (1 << j)) != 0 != (i & (1 << k)):
                    d[i] = max(d[i], d[i ^ (1 << j) ^ (1 << k)] + (a[j] ^ a[k]))

    return d[-1]


def _start():
    ret = main()

    if ret is not None:
        if isinstance(ret, List) or isinstance(ret, Tuple):
            print(*ret)
        else:
            print(ret)


if __name__ == '__main__':
    _start()