/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.19 21:30:19
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    int n;cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    int ans = 0;
    for (int i = 0; i < n - 1; i++) {
        for (int j = i + 1; j < n; j++) {
            ans = max(ans,a[i] ^ a[j]);
        }
    }
    cout << ans << endl;
    return 0;
}