#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define rep2(i,m,n) for (int i = m; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
template <class T> void chmin(T &a, const T &b) noexcept { if (b < a) a = b; }
template <class T> void chmax(T &a, const T &b) noexcept { if (a < b) a = b; }
void debug_out() { cout << "\n"; }
template <class T, class... Args>
void debug_out(const T &x, const Args &... args) { cout << x << " "; debug_out(args...);}
#ifdef _DEBUG
  #define debug(...) debug_out(__VA_ARGS__)
#else
  #define debug(...) 
#endif

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(15);
  int n;
  cin >> n;
  vector<ll> a(n);
  rep(i,n) cin >> a[i];
  ll ans = 0;
  rep(i,n) rep2(j,i+1,n) {
    chmax(ans, a[i]^a[j]);
  }
  cout << ans << endl;
  return 0;
}