#include <bits/stdc++.h>
using namespace std;

int main()
{
	int N;
	cin >> N;
	vector<long long> A( N );
	for( int i = 0; i < N; i++ ) {
		cin >> A[i];
	}

	long long 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;
}