#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
void solve() {
  long long int n;
  cin >> n;
  long long int a[n];
  long long int ans = 0;
  long long int left[n], right[n];
  memset(left, -1, sizeof(left));
  stack<long long int> s;
  for (long long int i = 0; i < n; i++) {
    cin >> a[i];
    right[i] = n;
    while (!s.empty() && a[s.top()] < a[i]) s.pop();
    if (!s.empty()) left[i] = s.top();
    s.push(i);
  }
  while (!s.empty()) s.pop();
  for (long long int i = n - 1; i >= 0; i--) {
    while (!s.empty() && a[s.top()] < a[i]) s.pop();
    if (!s.empty()) right[i] = s.top();
    s.push(i);
  }
  for (long long int i = 0; i < n; i++) {
    long long int start = left[i] + 1;
    long long int end = right[i] - 1;
    for (long long int j = i - 1; j >= start; j = left[j]) {
      ans = max(ans, a[i] ^ a[j]);
    }
    for (long long int j = i + 1; j <= end; j = right[j]) {
      ans = max(ans, a[i] ^ a[j]);
    }
  }
  cout << ans << "\n";
}
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  srand(time(NULL));
  ;
  int t = 1;
  for (int i = 1; i <= t; i++) {
    solve();
  }
}
