#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<unordered_map>
#include<random>
#include<array>
#include<cassert>
using namespace std;
#define INF ((1LL<<60)-1)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()



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

	int n;
	int a[2000];
	cin >> n;
	rep(i, n)cin >> a[i];
	int ans = 0;

	rep(j,n)rep(i,j) {
		ans = max(ans, a[i] ^ a[j]);
	}

	cout << ans << endl;


	
	return 0;
}