#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
#define rep(i,s,e) for(int (i) = (s);(i) <= (e);(i)++)

int N;
vector<i64> A;

i64 dp[1 << 15];

int main(){
  cin >> N;
  A.resize(N);
  rep(i,0,N - 1){
    cin >> A[i];
  }

  rep(i,0,(1 << 15) - 1){
    dp[i] = -1e9;
  }
  dp[0] = 0;

  for(int s = 1;s < (1 << N);s++){
    if(__builtin_popcount(s) % 2 == 1) continue;
    for(int i = 0;i < N;i++){
      for(int j = 0;j < N;j++){
        if(i == j) continue;
        if(!(s & (1 << i))) continue;
        if(!(s & (1 << j))) continue;

        int t = s;
        t = t & ~(1 << i);
        t = t & ~(1 << j);

        dp[s] = max(dp[s],dp[t] + (A[i] ^ A[j]));
      }
    }
  }

  cout << dp[(1 << N) - 1] << endl;
}