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

int main() {
    int N;
    cin >> N;
    int A[N];
    for (int i = 0; i < N; i++) cin >> A[i];
    int DP[(1 << N)] = {};
    for (int bits = 0; bits < (1 << N); bits++) {
        if (__builtin_parity(bits)) continue;
        vector<int> matched;
        for (int i = 0; i < N; i++) {
            if (bits & (1 << i)) {
                matched.push_back(i);
            }
        }
        for (size_t i = 0; i < matched.size(); i++) {
            for (size_t j = i + 1; j < matched.size(); j++) {
                DP[bits] = max(DP[bits], (A[matched[i]] ^ A[matched[j]]) + DP[bits ^ (1 << matched[i]) ^ (1 << matched[j])]);
            }
        }
    }
    cout << DP[(1 << N) - 1] << endl;
}