#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e6+10,M=1e9+10;
int a[N],s[N];
signed main()
{
 int n;
 cin>>n;
 for(int i=1;i<=n;i++)
 {
 	cin>>a[i];
 	s[i]=s[i-1]^a[i];
 } 
 int ma=M;
 for(int i=1;i<=30;i++)
 {
 	for(int j=1;j<=30;j++)
 	{
	 	for(int k=1;k<=n;k++)
	 	{
	 		if(k-1+i>n-1)continue;
	 		if(k+i-1+j>n)continue;
		   if((int)(s[k-1]^s[k-1+i])>(int)(s[k+i-1]^s[k+i-1+j])&&ma>i-1+j-1)
		   {
		     ma=i-1+j-1;
//		     cout<<i<<" "<<j<<'\n';
//		     cout<<(int)(s[k-1]^s[k-1+i])<<" "<<(int)(s[k+i-1]^s[k+i-1+j])<<'\n';
		   }	
		}
	}
 }
 if(ma==M)cout<<-1;
 else cout<<ma;
}//