#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n);
  REP (i, n) cin >> a[i];
  
  int ret = 0;
  REP (i, n) REP (j, i) ret = max(ret, a[i] ^ a[j]);
  cout << ret << endl;
  
  return 0;
}