N = int(input())
A = [int(x) for x in input().split()]

dp = [0]*(2**N)
for bit in range(2**N):
  for x in range(N-1):
    if bit>>x & 1:
      continue
    for y in range(x+1, N):
      if bit>>y & 1:
        continue
      bn = bit+2**x+2**y
      dp[bn] = max(dp[bn], dp[bit] + (A[x] ^ A[y]))

print(dp[2**N-1])