#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

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