#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define rep(i,a,b) for(ll i = a; i < b; i++)
#define REP(i,a,b) for(ll i = a; i <=b; i++)
#define fore(i,a) for(auto &i : a)
#define all(x) (x).begin(),(x).end()
#define fix(i) fixed << setprecision(i)
#define nextp(v) next_permutation(all(v))



template<class T>bool chmax(T& a, const T& b) { if(a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if(b < a) { a = b; return 1; } return 0; }

using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pq = priority_queue<int>;
using pqll = priority_queue<ll>;



const ll INF = LLONG_MAX/2;
const ll MOD = 1000000007;





int main() {
  int N; cin >> N;
  
  vector<int> a(N);
  rep(i,0,N) cin >> a[i];
  
  int Ans = 0;
  rep(i,0,N-1) rep(j,0,N) {
    int S = (a[i] ^ a[j]);
    chmax(Ans, S);
  }
  
  printf("%d\n", Ans);
}