int N, A[19];

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

{
    rd(N,A(N));
    cout << dfs(0) << endl;
}