#include<iostream>
#include<set>
#include <bitset>
#include<queue>
#include<vector>
#include<map>
#include<stack>
#include <cstdio>
#include<algorithm>
#include <sstream>
#include<string>
#include<string.h>
#include <cmath>
#include <iomanip>
#include <string>
#include<list>
#include <limits>
#include <numeric>
#include <type_traits>
#include<bitset>
#define int long long
#define ll long long
#define mod  1000000007
#define inf 1e17
#define rep(i,j,n) for(int i=j;i<n;i++)
#define P pair<int,int>
double pi = 3.141592653589793;
using namespace std;
//ここから始めよう
int dp[1<<20];//この集合のときの最大値
int n;int a[20];
int cnt=0;
int solve(int bit){cnt++;
    int res=dp[bit];
    if(~res)return res;
    res=0;
    if(bit==0)return 0;
    rep(i,0,n-1){
        rep(j,i+1,n){
            if(!(bit&(1<<i))||!(bit&(1<<j)))continue;
            int h=bit&~(1<<i);h=h&~(1<<j);
            res=max(res,solve(h)+(a[i]^a[j]));
        }
    }
    dp[bit]=res;
   //cout<<res<<" "<<bit<<endl;
    return dp[bit];
}
signed main(){
    cin>>n;
    rep(i,0,n)cin>>a[i];
    memset(dp,-1,1<<18);
    cout<<solve((1<<n)-1)<<endl;
    //cout<<cnt<<endl;
    return 0;
}