#https://yukicoder.me/problems/no/698

def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10000000)
    from collections import Counter, deque
    #from collections import defaultdict
    from itertools import combinations, permutations, accumulate
    #from itertools import product
    from bisect import bisect_left,bisect_right
    import heapq
    from math import floor, ceil
    #from operator import itemgetter

    #inf = 10**17
    #mod = 10**9 + 7

    N = int(input())
    a = list(map(int, input().split()))

    #dp[s]:sは作成済みのペア
    #         dp[s]はその時の戦闘力
    dp = [0]*(1<<N)

    for s in range(1<<N):
        #1が奇数個の場合はスルー
        cnt = 0
        for i in range(N):
            if (s>>i) & 1:
                cnt += 1
        if cnt%2 != 0:
            continue

        
        #誰がペアを作るか
        for i in range(N):
            cur = 0
            if (s>>i) == 0:
                #片方の戦闘力
                cur = a[i]
                new_s = s|1<<i
                dp[new_s] = dp[s]
                #ペアを作る相手とその時の戦闘力
                for j in range(N):
                    if (new_s>>j) & 1 == 0:
                        dp[new_s|1<<j] = max(dp[new_s|1<<j], dp[new_s]+(cur^a[j]))
    print(dp[-1])

if __name__ == '__main__':
    main()