#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main()
{
    ll N;
    cin >> N;
    vector<ll> A(N), dp(1LL << N, 0);
    for (ll i = 0; i < N; i++)
        cin >> A[i];
    for (ll bit = 0; bit < (1LL << N); bit++)
    {
        for (ll i = 0; i < N; i++)
        {
            for (ll j = i + 1; j < N; j++)
            {
                if (!(bit & (1LL << i)) && !(bit & (1LL << j)))
                {
                    dp[bit + (1 << i) + (1 << j)] = max(dp[bit] + (A[i] ^ A[j]), dp[bit + (1 << i) + (1 << j)]);
                }
            }
        }
    }
    cout << dp[(1 << N) - 1] << endl;
}