#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <string>
#include <vector>
#include <queue>
#include <cmath>
#include <stack>
#include <set>
#include <map>
typedef long long ll;
using namespace std;

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

  int dp[1<<N];
  fill(dp,dp+(1<<N),0);

  for(int i=0;i<(1<<N);i++){
    for(int j=0;j<N;j++){
      for(int k=j+1;k<N;k++){
        if(!(i & (1 << j)) && !(i & (1 << k))){
          dp[i + (1<<j) + (1<<k)] = max(dp[i + (1<<j) + (1<<k)], dp[i] + (a[j] ^ a[k]));
        }
      }
    }
  }

  cout << dp[(1 << N) - 1] << endl;
  return 0;
}