#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<long long>;

#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define rep(i, a, b) for (int i = (a); i < (b); i++)

mt19937 rng(random_device{}());

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int n;

	cin >> n;

	vector <ll> a (n);

	rep(i, 0, n){
		cin >> a[i];
	}

	sort(all(a));
	
	ll result = 0;

	rep(i, 0, n){
		rep(j, 0, n){
			ll temp = a[i] ^ a[j];

			if(temp > result)
				result = temp;
		}
	}

	cout << result << "\n";
	
	return 0;
}