import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int[] arr = new int[n];
    	for (int i = 0; i < n; i++) {
    	    arr[i] = sc.nextInt();
    	}
    	int[] dp = new int[1 << n];
    	HashSet<Integer> pair = new HashSet<>();
    	for (int i = 1; i < (1 << n); i++) {
    	    int count = getPopcount(i);
    	    if (count == 2) {
    	        int base = 0;
    	        int value = i;
    	        for (int j = 0; j < n; j++) {
    	            if (value % 2 == 1) {
    	                base ^= arr[j];
    	            }
    	            value /= 2;
    	        }
    	        dp[i] = base;
    	        pair.add(i);
    	    } else if (count % 2 == 0) {
    	        int max = 0;
    	        for (int x : pair) {
    	            if ((x & i) != x) {
    	                continue;
    	            }
    	            max = Math.max(max, dp[x] + dp[i ^ x]);
    	        }
    	        dp[i] = max;
    	    }
    	}
    	System.out.println(dp[(1 << n) - 1]);
	}
	
	static int getPopcount(int x) {
	    int count = 0;
	    while (x > 0) {
	        count += x % 2;
	        x /= 2;
	    }
	    return count;
	}
}