#include <iostream>
#include <vector>
#include <functional>

void solve() {
    int n;
    std::cin >> n;
    std::vector<int> xs(n);
    for (auto& x : xs) std::cin >> x;

    std::function<int(int, int)> dfs =
        [&](int b, int s) -> int {
        int i = 0;
        while ((b >> i) & 1) ++i;
        if (i == n) return s;

        int ret = 0;
        for (int j = i + 1; j < n; ++j) {
            if ((b >> j) & 1) continue;

            int ns = s ^ (xs[i] + xs[j]);
            int nb = b | (1 << i) | (1 << j);
            ret = std::max(ret, dfs(nb, ns));
        }
        return ret;
    };

    std::cout << dfs(0, 0) << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}