#include <bits/stdc++.h>
typedef unsigned long long ll;
#define INF 1000000000
using namespace std;
int main(void){
    int n;
    cin>>n;
    vector<int>A(n);
    for(int i=0;i<n;i++){
        cin>>A[i];
    }
    int dp[1<<14]={-1};
    dp[0]=0;
    for(int msk=0;msk<(1<<n);msk++){
        for(int a=0;a<n;a++){
            for(int b=a+1;b<n;b++){
                if(!(msk&(1<<a)) and !(msk&(1<<b))){
                       dp[msk+(1<<a)+(1<<b)]=max(dp[msk+(1<<a)+(1<<b)],dp[msk]+A[a]^A[b]);
                }
            }
        }
    }
    cout<<dp[(1<<n)-1]<<endl;
 
}