#include <iostream>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <algorithm>
#include <numeric>
#include <queue>
#include <cassert>
#include <cmath>
using namespace std;

int n;
long long a[20];
long long dp[20000];

void chmax(long long &a, long long b) {
  a = max(a, b);
}

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

  for (int s = 0; s < (1<<n); s++) {
    for (int i = 0; i < n; i++) {
      for (int j = i+1; j < n; j++) {
        if ((s&(1<<i)) == 0 && (s&(1<<j)) == 0) {
          chmax(dp[s|(1<<i)|(1<<j)], dp[s] + (a[i] ^ a[j]));
        }
      }
    }
  }
  cout << dp[(1<<n)-1] << endl;
}