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

int main(){
  int n; cin >> n;
  vector<ll> a(n);
  for(int i = 0; i < n; i++) cin >> a[i];
  ll ans = 0;
  for(int i = 0; i < n-1; i++){
    for(int j = i+1; j < n; j++){
      ans = max(ans, a[i]^a[j]);
    }
  }
  cout << ans << endl;
  return 0;
}