#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <cassert>
using namespace std;
using i64 = int64_t;
constexpr i64 mod = 1e9 + 7;
using vi = vector<i64>;
using vvi = vector<vi>;
using ii = pair<i64, i64>;
using vii = vector<ii>;

int n, as[14], dp[1 << 14];

int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> as[i];
    }
    
    for (int i = 0; i < (1 << n); i++) {
        for (int a = 0; a < n; a++) {
            for (int b = a + 1; b < n; b++) {
                if (!(i & (1 << a))) {
                    if (!(i & (1 << b))) {
                        dp[i | (1 << a) | (1 << b)] = max(dp[i | (1 << a) | (1 << b)], dp[i] + (as[a] ^ as[b]));
                    }
                }
            }
        }
    }
    cout << dp[(1 << n) - 1] << endl;
}