#include <bits/stdc++.h>
using namespace std;
 
#define fi first
#define se second
#define pb push_back
using vi = vector <int>;
using ll = long long;
using pii = pair <int, int>;
//~ const ll mod = 998244353;
const ll mod = 1e9 + 7;
ll qpow(ll a, ll b, ll m = mod) { ll r = 1, t = a;
	for(; b; b /= 2) { if(b & 1) r = r * t % m; t = t * t % m; } return r; }

const int N = 2e3 + 11;
int a[N];

int main() {
	ios :: sync_with_stdio(false);
	
	int n; cin >> n;
	for(int i = 0; i < n; i ++)
		cin >> a[i];
	
	int ans = 0;
	for(int i = 0; i < n; i ++)
		for(int j = i + 1; j < n; j ++)
			ans = max(ans, a[i] ^ a[j]);
	cout << ans << '\n';
}