int N, A[15];
int dp[1<<15];
{
    rd(N,A(N));
    REP(b, 1<<(N-1)){
        if (__builtin_popcountll(b)&1) continue;
        REP(i, N){
            if (b&(1<<i)) continue;
            REP(j, N){
                if (b&(1<<j)) continue;
                int b2 = b|(1<<i)|(1<<j);
                dp[b2] = max(dp[b2], dp[b]+(A[i]^A[j]));
            }
        }
    }
    wt(dp[(1<<N)-1]);
}