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

int main(){
    int N;
    cin >> N;
    vector<int> A(N);
    for (int& x : A) cin >> x;

    vector<int> dp(1<<N, -1);
    dp[0] = 0;
    for (int bit = 0; bit < (1<<N); bit++) if (dp[bit] != -1){
        int i = -1;
        for (int j = 0; j < N; j++){
            if (!(bit>>j&1)){
                i = j;
                break;
            }
        }
        if (i == -1) continue;
        for (int j = i+1; j < N; j++){
            if (bit>>j&1) continue;
            int nb = bit|(1<<i)|(1<<j);
            dp[nb] = max(dp[nb], dp[bit]^(A[i]+A[j]));
        }
    }

    cout << dp.back() << endl;
}