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

#ifdef LOCAL
#include "debug.h"
#else
#define DEBUG(...)
#endif

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> a(n);
  for (auto&& e : a) cin >> e;
  int res = 0;
  for (int j = 0; j < n; ++j) {
    for (int i = 0; i < j; ++i) {
      res = max(res, a[i] ^ a[j]);
    }
  }
  cout << res << '\n';
}