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

const long long inf=1e17;
int A[21];
int dp[1 << 21];

int main(void){
    long long n;
    cin >> n;

    for(long long i=0; i<n; i++){
          cin >> A[i];
    }

    dp[0]=0;
    for(long long msk=0;msk<(1<<n);msk++){
        for(long long a=0;a<n;a++){
            for(long long b=a+1;b<n;b++){
              if(!(msk&(1<<a))){
                if(!(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;
    return 0;
}