def bsf(x: int) -> int:
    assert x != 0
    return (x & -x).bit_length() - 1


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

dp = [-1] * (1 << N)
dp[0] = 0
for i in range(1 << N):
    if dp[i] == -1: continue
    pi = bsf(~i)
    for pj in range(pi+1, N):
        if i & (1 << pj): continue
        ni = i | (1 << pi) | (1 << pj)
        dp[ni] = max(dp[ni], dp[i] + (A[pi] ^ A[pj]))

ans = dp[(1 << N) - 1]
print(ans)