N = int(input())
A = [int(i) for i in input().split()]
DP = [0]*(1<<N)

def chmax(DP,i,j,k):
    DP[i+j] = DP[i]+k if DP[i+j]<DP[i]+k else DP[i+j]
    return;

N_bit = 1<<N
for i in range(N_bit):
    for a in range(N):
        for b in range(a+1,N):
            if((i & 1<<a | i & 1<<b) == 0):
                chmax(DP,i,(1<<a)+(1<<b),A[a]^A[b])
print(DP[-1])