#region Header
#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
import bisect
import heapq


def input():
    return sys.stdin.readline()[:-1]


# sys.setrecursionlimit(1000000)
#endregion

# _INPUT = """4
# 1 2 3 4
# """
# sys.stdin = io.StringIO(_INPUT)

def main():
    N = int(input())
    A = list(map(int, input().split()))

    dp = [[0] * (1<<N) for _ in range(N)]
    for i in range(1, N):
        for s in range(1<<i):
            
            # 選手i を用いない
            dp[i][s] = max(dp[i][s], dp[i-1][s])

            # 選手i を用いる
            for j in range(i):
                if s & (1<<j) == 0:
                    s1 = s | (1<<j) | (1<<i)
                    dp[i][s1] = max(dp[i][s1], dp[i-1][s] + (A[j] ^ A[i]))
    ans = dp[N-1][(1<<N)-1]
    print(ans)


if __name__ == '__main__':
    main()