#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
 int n; cin >> n;
 vector<int> a(n);
 for (int i = 0; i < n; i++) cin >> a[i];
 
 sort(a.begin(), a.end());

 int ans = 0;
 for (int i = 0; i < n; i++) ans =max(ans, a[i] ^ a[0]);

 cout << ans << endl;

 return 0;
}