#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  int N;
  cin >> N;
  int A[N];

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

  int dp[1 << N];
  memset(dp, 0, sizeof(dp));

  for (int i = 0; i < N / 2; ++i) {
    for (int mask = 0; mask < (1 << N); ++mask) {
      if (__builtin_popcount(mask) != 2 * i) continue;

      for (int s = 0; s < N; ++s) {
        if (mask >> s & 1) continue;

        for (int t = 0; t < N; ++t) {
          if (mask >> t & 1) continue;

          int nmask = mask | (1 << s) | (1 << t);
          dp[nmask] = max(dp[nmask], dp[mask] + (A[s] ^ A[t]));
        }
      }
    }
  }

  cout << dp[(1 << N) - 1] << endl;

  return 0;
}