from itertools import combinations
N = int(input())
A = list(map(int,input().split()))
dp = {}
for z in combinations(range(N),2):
    dp[z] = A[z[0]]^A[z[1]]
for n in range(4,N+1,2):
    for z in combinations(range(N),n):
        dp[z] = 0
        for y in combinations(z,2):
            z1 = list(z)
            z1.remove(y[0])
            z1.remove(y[1])
            z1 = tuple(z1)
            dp[z] = max(dp[z],dp[z1]+(A[y[0]]^A[y[1]]))
ans = tuple(range(N))
print(dp[ans])