#include <bits/stdc++.h>
using namespace std;
#include <atcoder/convolution>
#include <atcoder/modint>
using namespace atcoder;

//基本的にこれがなくてもうまくいくコードを心がけるが、念の為。時間ギリギリアウトの時は消してみる
#define int long long

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ldb;
typedef pair<int, int> pi;
typedef pair<long long, long long> pl;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<vector<int> > vvi;
typedef vector<vector<long long> > vvl;
typedef priority_queue<int> pq;
typedef priority_queue<int, vector<int>, greater<int> > pqg;
typedef priority_queue<long long> pql;
typedef priority_queue<long long, vector<long long>, greater<long long> > pqgl;

#define pb push_back
#define eb emplace_back
#define mp make_pair

#define all(obj) (obj).begin(), (obj).end()

#define reps(i, n, m) for (int i = (int)(n); i < (int)(m); i++)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = n; i >= 0; i--)

#define cbit(x) __builtin_popcountll(x)

#define minv(v) *min_element(v.begin(), v.end())
#define maxv(v) *max_element(v.begin(), v.end())

#define print(v)                       \
    for (auto k : v) cout << k << " "; \
    cout << endl;

#define yesno(bool)            \
    if (bool) {                \
        cout << "Yes" << endl; \
    } else {                   \
        cout << "No" << endl;  \
    }

//既存値aより新規値bが大きければ更新
template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
//既存値aより新規値bが小さければ更新
template <class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}

#define ednl endl  //打ち間違え用
#define enld endl
#define Endl endl

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
// int dx[8] = {1, 1, 1, 0, -1, -1, -1, 0};
// int dy[8] = {-1, 0, 1, 1, 1, 0, -1, -1};

// const int MOD = 998244353;  //素数(223*119+1)
// const int MOD = 1000000007;  //素数

// using mint = modint998244353;
// using mint = modint1000000007;
// using mint = static_modint<1000000009>;
////////////////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////////////////
signed main() {
    int n;
    cin >> n;
    vi a(n);
    rep(i, n) {
        cin >> a[i];
    }
    vl d((1 << n), 0);
    d[0] = 0;
    rep(i, 1 << n) {
        if (cbit(i) % 2 == 1) continue;
        rep(j, n) {
            reps(k, j + 1, n) {
                if ((i & (1 << j)) && (i & (1 << k))) {
                    int l = i & ~(1 << j);
                    l = l & ~(1 << k);
                    d[i] = max(d[i], d[l] + (a[j] ^ a[k]));
                }
            }
        }
    }
    cout << d[(1 << n) - 1] << endl;
}