n = gets.chomp.to_i
a = gets.chomp.split(" ").map(&:to_i)
bit = 1 << n
max = 0
dp = Array.new(1<<n,0)
0.upto(bit-1) do |i|
    number = 0
    team = 0
    0.upto(n) do |j|
        ij = i >> j
        if ij & 1 == 1
            team += 1
        end
    end
    next if team % 2 == 1
    #print "iは"+"#{i}" + " "+" teamは" + "#{team}" + "\n"
    0.upto(n-2) do |x|
        next if 1 << x & i != 0
        (x+1).upto(n-1) do |y|
            next if 1 << y & i != 0
            xx = 1 << x
            yy = 1 << y
            dp[i|xx|yy] = [dp[i|xx|yy],dp[i] + (a[x] ^ a[y])].max            
        end
    end
    #ここまではOK
end
puts dp[-1]