int N, A[19];

int dfs(vector<int>& flg, int val = 0){
    int i = 0;
    while (i < N && flg[i]) ++i;
    if (i == N) return val;
    flg[i] = 1;
    int best = 0;
    REP(j,i+1,N){
        if (flg[j]) continue;
        flg[j] = 1;
        best = max(best, dfs(flg, val^(A[i]+A[j])));
        flg[j] = 0;
    }
    flg[i] = 0;
    return best;
}

{
    rd(N,A(N));
    
    vector<int> flg;
    flg.resize(N);
    cout << dfs(flg) << endl;
}