#include <iostream>
#include <vector>
#include<iomanip>
#include<functional>
#include<algorithm>
#include<deque>
#include<math.h>
#include<set>
#include<cstdio>
#include<string>
#include<queue>
#include<complex>
#include<numeric>
#include<stack>
#include<unordered_map>
#include<map>
#include <cassert>
#include<random>
using namespace std;
#define rep(i,n) for(int i = 0;i<n;i++)
#define req(i,n) for(ll i = 1;i<=n;i++)
#define rrep(i,n) for(int i = n-1;i>=0;i--)
#define ALL(a) a.begin(),a.end()
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
typedef long long ll;
typedef long double ld;
const ll mod = 1e9 + 7;
const ll MOD = 998244353;
int main() {
    int n; cin >> n;vector<int> a(n);
    rep(i, n) cin >> a[i];
    vector<int> dp(1 << n, -1e9); dp[0] = 0;
    rep(bit, 1 << n) {
        rep(i, n) rep(j, i) {
            if ((!((bit >> i) & 1)) && (!((bit >> j) & 1))) {
                chmax(dp[bit + (1 << i) + (1 << j)], dp[bit] + (a[i]^a[j]));
            }
        }
    }cout << dp[(1 << n)-1] << endl;
}