import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] a = new int[n];
    for(int i = 0; i < n; i++) {
      a[i] = sc.nextInt();
    }
    int p = (int)Math.pow(2, n);
    int[] dp = new int[p];

    for(int i = 1; i < p; i++) {
      for(int j = 0; j < n; j++) {
        if((i & (1 << j)) != 0) {
          for(int k = j + 1; k < n; k++) {
            if((i & (1 << k)) != 0) {
              int i1 = i - (1 << j) - (1 << k);
              int t = dp[i1];
              t += (a[j] ^ a[k]);
              dp[i] = Math.max(dp[i], t);
            }
          }
        }
      }
    }
    System.out.println(dp[p - 1]);
  }
}