#include <bits/stdc++.h>
#ifdef _DEBUG
#include "debug.hpp"
#else
#define debug(...)
#endif
#define REP(i, m, n) for(int i = (int)(m); i < (int)(n); ++i)
#define rep(i, n) REP(i, 0, n)
using namespace std;
using ll = long long; using ld = long double; using pll = pair<ll, ll>;
const int INF = 1<<30; const ll LINF = 1LL<<60; const ld PI = 3.1415926535897932;
template<class T, class U> inline bool chmax(T &a, const U &b) { if(a < b) { a = b; return true; } return false; }
template<class T, class U> inline bool chmin(T &a, const U &b) { if(a > b) { a = b; return true; } return false; }



int main() {
  cin.tie(0); ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<ll> a(n);
  rep(i, n) cin >> a[i];
  ll ans = 0;
  rep(i, n) REP(j, i+1, n) {
    chmax(ans, a[i]^a[j]);
  }
  cout << ans << '\n';
  return 0;
}