import java.util.*;
import java.io.*;

public class Main {
    static int n;
    static int[][] dp;
    static int[] scores;
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", n);
        scores = new int[n];
        for (int i = 0; i < n; i++) {
            scores[i] = Integer.parseInt(line[i]);
        }
        dp = new int[n / 2 + 1][(int)(Math.pow(2, n))];
        System.out.println(dfw(n / 2, (int)(Math.pow(2, n)) - 1));
    }
    
    static int dfw(int idx, int key) {
        if (idx == 0) {
            return 0;
        }
        if (dp[idx][key] != 0) {
            return dp[idx][key];
        }
        int max = 0;
        for (int i = 0; i < n - 1; i++) {
            int x = (int)(Math.pow(2, i));
            if ((key & x) == 0) {
                continue;
            }
            for (int j = i + 1; j < n; j++) {
                int y = (int)(Math.pow(2, j));
                if ((key & y) == 0) {
                    continue;
                }
                max = Math.max(max, dfw(idx - 1, key ^ (x | y)) + (scores[i] ^ scores[j]));
            }
        }
        dp[idx][key] = max;
        return max;
    }
}