#include<iostream>
using namespace std;

int n, ans = 0, a[14] = {};

void dfs(int score, int bitset){
    if(bitset == (1<<n)-1){
        ans = max(ans, score);
        return;
    }

    for(int i = 0; i < n; i++){
        if(~bitset & 1<<i){
            for(int j = i+1; j < n; j++){
                if(~bitset & 1<<j){
                    dfs(score ^ (a[i] + a[j]), bitset|1<<i|1<<j);
                }
            }
        }
    }
}

int main(){
    cin >> n;
    for(int i = 0; i < n; i++)  cin >> a[i];
    dfs(0, 0);
    cout << ans << endl;
}