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

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i,n) cin >> a[i];

  int ans = 0;
  rep(i,n)rep(j,n) ans = max(ans, a[i]^a[j]);
  cout << ans << endl;


}