#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <typeinfo>
#include <numeric>
#include <functional>
#include <unordered_map>
#include <bitset>


using namespace std;
using ll = long long;
using ull = unsigned long long;

const ll INF = 1e16;
const ll MOD = 1e9 + 7;

#define REP(i, n) for(ll i = 0; i < n; i++)





int main() {
    ll n;
    cin >> n;
    
    vector<ll> a(n);
    REP(i, n){
        cin >> a[i];
    }
    
    vector<ll> dp(1 << n);
    REP(i, 1 << n){
        ll c = 0;
        for(ll j = i; j > 0; j >>= 1){
            if(j & 1)c++;
        }
        if(c & 1)continue;
        
        REP(j, n - 1){
            if((i >> j) & 1){
                for(ll k = j + 1; k < n; k++){
                    if((i >> k) & 1){
                        dp[i] = max(dp[i], dp[i ^ (1 << j) ^ (1 << k)] + (a[j] ^ a[k]));
                    }
                }
            }
        }
    }
    
    cout << dp[(1 << n) - 1] << endl;
}