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

signed main() {
  ios::sync_with_stdio(false);

  int N;
  cin >> N;

  vector<int> A(N);
  for (int i = 0; i < N; ++i) cin >> A[i];

  vector<int> dp(1 << N);
  for (int s = 0; s + 1 < 1 << N; ++s) {
    if (__builtin_popcount(s) & 1) continue;
    int l = __builtin_ctz(~s);
    for (int i = 0; i < N; ++i)
      if (~s >> i & 1)
        if (i != l)
          dp[s | 1 << l | 1 << i] = max(dp[s | 1 << l | 1 << i], dp[s] + (A[l] ^ A[i]));
  }

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

  return 0;
}