#include <bits/stdc++.h>
using namespace std;
long long arr[100009];
vector<long long> lock;
int main() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> arr[i];
  }
  if (n == 2) {
    cout << (arr[1] ^ arr[2]) << endl;
    return 0;
  }
  long long ans = 0;
  stack<long long> msla;
  msla.push(arr[1]);
  for (int i = 2; i <= n; i++) {
    long long cuel = arr[i];
    ans = max(ans, (arr[i] ^ arr[i - 1]));
    long long kala = -1;
    while (true) {
      if (msla.empty() || (msla.top() > cuel)) {
        if (!msla.empty()) kala = msla.top();
        msla.push(cuel);
        break;
      }
      long long yopa = msla.top();
      if (yopa < cuel) {
        msla.pop();
      }
    }
    if (kala != -1) {
      ans = max(ans, cuel ^ kala);
    }
  }
  stack<long long> msla2;
  msla2.push(arr[n]);
  for (int i = n - 1; i >= 1; i--) {
    long long cuel = arr[i];
    ans = max(ans, (arr[i] ^ arr[i + 1]));
    long long kala = -1;
    while (true) {
      if (msla2.empty() || (msla2.top() > cuel)) {
        if (!msla2.empty()) kala = msla2.top();
        msla2.push(cuel);
        break;
      }
      long long yopa = msla2.top();
      if (yopa < cuel) {
        msla2.pop();
      }
    }
    if (kala != -1) {
      ans = max(ans, cuel ^ kala);
    }
  }
  cout << ans << endl;
  return 0;
}
