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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int[] values = new int[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextInt();
        }
        int[] dp = new int[1 << n];
        for (int i = 1; i < (1 << n); i++) {
            if (getPop(i) % 2 == 1) {
                continue;
            }
            for (int j = 0; j < n; j++) {
                if ((i & (1 << j)) == 0) {
                    continue;
                }
                for (int k = j + 1; k < n; k++) {
                    if ((i & (1 << k)) == 0) {
                        continue;
                    }
                    dp[i] = Math.max(dp[i], (values[j] ^ values[k]) + dp[i ^ (1 << j) ^ (1 << k)]);
                }
                break;
            }
        }
        System.out.println(dp[(1 << n) - 1]);
    }
    
    static int getPop(int x) {
        int pop = 0;
        while (x > 0) {
            pop += x % 2;
            x >>= 1;
        }
        return pop;
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}