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

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr); cout.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

int main() {
    int n; cin >> n;
    auto a = vec<int>(uns, n);
    for (auto &e : a) cin >> e;

    auto popcount = [](auto x) {
        return bitset<sizeof(x) * CHAR_BIT>(x).count();
    };

    auto dp = vec<int>(0, 1 << n);
    for (int i = 0; i < (1 << n); ++i) {
        if (popcount(i) % 2 != 0) continue;
        for (int j = 0; j < n; ++j) {
            for (int k = j + 1; k < n; ++k) {
                if ((i & (1 << j)) || (i & (1 << k))) continue;
                chmax(dp[i | (1 << j) | (1 << k)], dp[i] + (a[j] ^ a[k]));
            }
        }
    }

    cout << dp[(1 << n) - 1] << endl;
}