#include<bits/stdc++.h>

#define INF 1e9
#define llINF 1e18
#define MOD 1e9+7
#define pb push_back
#define mp make_pair 
#define F first
#define S second
#define ll long long
using namespace std;
int n;
vector<ll>vll(50);
ll memo[60000]={};
ll dfs(int used,ll sum,ll ma){
  if(memo[used]>ma)return memo[used];
  memo[used]=ma;
  if(used==((1<<n)-1)){
    return ma=max(ma,sum);
  }
  for(int i=0;i<n;i++){
    for(int j=i+1;j<n;j++){
      if((used&(1<<i))||(used&(1<<j)))
	continue;
      ma=max(dfs((used+(1<<i)+(1<<j)),sum^(vll[i]+vll[j]),ma),ma);
    }
  }
  return ma;
}
int main(){
  cin>>n;
  for(int i=0;i<n;i++)
    cin>>vll[i];
  cout<<dfs(0,0,0)<<endl;
  return 0;
}