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

stack = [[[], 0]]
ans = 0
until stack.empty?
  e, bit = stack.pop
  if e.size == n / 2
    ans = [ans, e.reduce{|x, y| x ^ y}].max
  else 
    (0...n).each do |x|
      ((x + 1)...n).each do |y|
        stack << [[*e, a[x] + a[y]], (bit | (1 << x) | (1 << y))] if (bit & (1 << x)) == 0 && (bit & (1 << y)) == 0
      end
    end
  end
end

puts ans