#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll dx[] = {0, 0, 1, -1};
ll dy[] = {1, -1, 0, 0};
void solve() {
  ll n;
  cin >> n;
  vector<ll> v(n);
  for (ll i = 0; i < (n); ++i) cin >> v[i];
  vector<pair<ll, ll>> aux(n);
  ll i = n - 1;
  stack<ll> s;
  while (i >= 0) {
    while (!s.empty() && s.top() < v[i]) s.pop();
    if (s.empty())
      aux[i].first = -1;
    else
      aux[i].first = s.top();
    s.push(v[i]);
    i--;
  }
  i = 0;
  while (!s.empty()) s.pop();
  while (i < n) {
    while (!s.empty() && s.top() < v[i]) s.pop();
    if (s.empty())
      aux[i].second = -1;
    else
      aux[i].second = s.top();
    s.push(v[i]), i++;
  }
  ll res = 0;
  for (ll i = 0; i < (n); ++i) {
    if (aux[i].first != -1) res = max(res, aux[i].first ^ v[i]);
    if (aux[i].second != -1) res = max(res, aux[i].second ^ v[i]);
  }
  cout << res << "\n";
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  ll t = 1;
  while (t--) solve();
  return 0;
}
