#!/usr/bin/python
# -*- coding: utf-8 -*-

# import
from sys import stdin, setrecursionlimit
setrecursionlimit(10**8)

def int_map():
    return map(int,input().split())

def int_list():
    return list(map(int,input().split()))

def int_mtx(N):
    x = [list(map(int, stdin.readline().split())) for _ in range(N)]
    return x

def str_mtx(N):
    x = [list(stdin.readline()[:-1]) for _ in range(N)]
    return x

def print_space(l):
    return print(" ".join([str(x) for x in l]))



"""    main code    """

N = int(input())
A = int_list()

dp = [0 for _ in range(2**N)]

for s in range(2**N):
    for u in range(N):
        for v in range(u+1,N):
            if s >> u & 1 == 0 and s >> v & 1 == 0:
                dp[s+2**u+2**v] = max(dp[s+2**u+2**v], dp[s] + (A[u]^A[v]))

print(dp[2**N-1])