n = int(input())
a = list(map(int, input().split()))

pairs = []
used = [False for _ in range(n)]

def dfs():
  if len(pairs) == n // 2:
    ans = 0
    for x in pairs:
      ans ^= x
    return ans
  else:
    for l in range(n):
      if used[l]:
        continue
      used[l] = True

      ans = 0
      for r in range(l + 1, n):
        if used[r]:
          continue

        used[r] = True
        pairs.append(a[l] + a[r])
        ans = max(ans, dfs())
        pairs.pop()
        used[r] = False

      used[l] = False
      return ans

print(dfs())