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

int n, d[20];
long long memo[100000];

long long dfs(int a, int b){
  if(a == n) return 0;
  if(memo[b] != -1) return memo[b];

  long long ret = 0;
  for(int i = 0;i < n-1;i++){
    for(int j = i+1;j < n;j++){
      if((b & (1 << i)) == 0 && (b & (1 << j)) == 0){
        ret = max(ret, dfs(a+2, b | (1 << i) | (1 << j)) + (d[i] ^ d[j]));
      }
    }
  }
  return memo[b] = ret;
}

int main(){
  cin >> n;
  for(int i = 0;i < n;i++) cin >> d[i];
  memset(memo,-1,sizeof(memo));
  cout << dfs(0, 0) << endl;
  return 0;
}