#include <iostream>
#include <algorithm>
#define MAX_N 14

using namespace std;
int A[MAX_N];
int dp[1 << MAX_N];

int main(){
    int N;
    cin >> N;
    for(int i=0; i<N; i++) cin >> A[i];
    for(int k=0; k<(1<<N); k++){
        for(int j=0; j<N;j++){
            for(int i=j+1; i<N;i++){
                if(!(k&(1<<j))&&!(k&(1<<i))){
                    dp[k+(1<<j)+(1<<i)] = max(dp[k+(1<<j)+(1<<i)], dp[k]+(A[i]^A[j]));
                }
            }
        }
    }
    cout << dp[(1<<N)-1] << endl;
}