#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int mod = 1e9 + 7;
const int inf = (1 << 30) - 1;
const ll infll = (1LL << 61) - 1;
#define fast() ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#define digit(N) cout << fixed << setprecision((N))

int N;

int main()
{
    cin >> N;
    vector<int> dp(1 << N), a(N);

    for (int i = 0; i < N; i++)
    {
        cin >> a[i];
    }

    for (int bit = 0; bit < (1 << N); bit++)
    {
        for (int i = 0; i < N; i++)
        {
            for (int j = i + 1; j < N; j++)
            {
                if (!(bit & (1 << i)) && !(bit & (1 << j)))
                {
                    dp[bit + (1 << i) + (1 << j)] = max(dp[bit + (1 << i) + (1 << j)], dp[bit] + (a[i] ^ a[j]));
                }
            }
        }
    }
    cout << dp[(1 << N) - 1] << "\n";
}