n = gets.to_i
a = gets.split.map(&:to_i)

dp = Array.new(2 ** n, 0)
dp.size.times do |bit|
  (0...n).each do |x|
    ((x + 1)...n).each do |y|
      next unless (bit & (1 << x)) == 0 && (bit & (1 << y)) == 0
      nxt = bit | (1 << x) | (1 << y)
      dp[nxt] = [dp[nxt], dp[bit] ^ (a[x] + a[y])].max
    end
  end
end

p dp.last