#include <bits/stdc++.h>
using namespace std;
 
#define REP(i, n) for (ll i = 0; i < n; i++)
#define REPR(i, n) for (ll i = n; i >= 0; i--)
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define FORR(i, m, n) for (ll i = m; i >= n; i--)
#define REPO(i, n) for (ll i = 1; i <= n; i++)
#define ll long long
#define INF (ll)1 << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(), n.end()
#define MOD 1000000007
#define P pair<ll, ll>


int main() {
    ll n;
    cin >> n;
    vector<ll> s(n);
    REP(i, n){
        cin >> s[i];
    }
    ll ans = 0;
    REP(i, n){
        FOR(j, i + 1, n){
            ans = max(ans, s[i] xor s[j]);
        }
    }
    cout << ans << endl;
}