#include <cstdio>
#include<iostream>
#include <algorithm>
#include <cstring>
using namespace std;
int main()
{
	freopen("xor_equ.in","r",stdin);
	freopen("xor_equ.out","w",stdout);
	int n;
	cin>>n;
	long long a[10001],sum[10001]={0},ans=0;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	for(int i=1;i<=n;i++)
	{
		for(int j=i+1;j<=n;j++)
		{
			sum[j]=a[i] xor a[j];
		}
		for(int j=n;j>=i;j--)
		{
			ans=max(ans,sum[j]);
		}
		memset(sum,0,sizeof(sum));
	}
	cout<<ans<<endl;
	return 0;
}