n = gets.chomp.to_i
a = gets.chomp.split(" ").map(&:to_i)
arr = [*0..(n/2)-1]
max = 0
arr.repeated_permutation(n) do |i|
    ans = 0
    hash = Hash.new(0)
    i.each do |j|
        hash[j] += 1
    end
    ok = true
    i.each do |k|
        if hash[k] != 2
            ok = false
        end
    end
    if ok
        group = Array.new(n/2).map{Array.new()}
        #p group
        i.each_with_index do |item,index|
            group[item] << a[index]
        end
        ans = 0
        group.each do |i,j|
            ans += i ^ j
        end
    end
    max = [max,ans].max
end
puts max