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


int dfs(int rem, int score, const vector<int>& As){
    if (rem == 0) return score;
    int record = score;
    for (int i = 0; i < As.size() - 1; ++i){
        if ((rem & (1 << i)) == 0) continue;
        rem ^= (1 << i);
        for (int j = i + 1; j < As.size(); ++j){
            if ((rem & (1 << j)) == 0) continue;
            record = max(record, dfs(rem ^ (1 << j), score + (As[i] ^ As[j]), As));
        }
        break;
    }
    return record;
}


int main() {
    int N;
    cin >> N;
    vector<int> As(N);
    for (auto & a : As) cin >> a;
    int rem = (1 << N) - 1;
    cout << dfs(rem, 0, As) << endl;

    return 0;
}