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

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)   FOR(i,0,n)
#define ALL(a)     (a).begin(),(a).end()
#define RALL(a)     (a).rbegin(),(a).rend()
#define PRINT(a)   cout << (a) << endl

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second

#define debug(x) cerr << x << " " << "(L:" << __LINE__ << ")" << '\n';

using ll = long long int;
using P = pair<int,int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using pii = pair<int, int>;

template <typename T> using PQ = priority_queue<T>;
template <typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

const int INF = 1001001001;
const ll LINF = 1001001001001001001ll;
const int MOD = 1e9 + 7;

int main(){
  int n;
  cin >> n;
  vector<ll> a(n);
  REP(i,n)cin >> a[i];

  vector<ll> dp(1<<n,-1);

  dp[0]=0;
  REP(s, (1<<n)){
    if(dp[s]==-1)continue;

    REP(x,n)REP(y,x){
      if((s & (1<<x)) || (s & (1<<y)))continue;
      int ss = s;
      ss |= (1<<x);
      ss |= (1<<y);
      chmax(dp[ss] , dp[s] + (a[x] ^ a[y]));
    }
  }

  cout << dp[(1<<n)-1] << endl;

}