#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<map>
#include<stack>
#include<cmath>
#include<iomanip>
#include<set>
#include<numeric>
#include<sstream>
#include<random>
#include<cassert>
#include<list>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rrep(i, st, n) for (int i = st; i < n; ++i)
using pii = pair<int, int>;
const int inf = 1e9 + 7;
int dy[] = {1, 1, 0, -1, -1, 0};
int dx[] = {1, 0, -1, -1, 0, 1};
#define ceil(a, b) a / b + !!(a % b)
#define chmax(a, b) a = max(a, b)

int main() {
    int n;
    cin >> n;
    int A[n];
    rep(i, n) cin >> A[i];
    int dp[1 << n];
    rep(i, (1 << n)) dp[i] = 0;
    rep(i, (1 << n)) {
        rep(a, n) rrep(b, a + 1, n) if (!(i & (1 << a)) && !(i & (1 << b))) {
            chmax(dp[i + (1 << a) + (1 << b)] , dp[i] + (A[a] ^ A[b]));
        }
    }
    cout << dp[(1 << n) - 1] << endl;
}