#include<stdio.h>
#define v 5002

int n,l,b[v][v],q,inc;
long c[v],max;

void citire()
{
freopen("secv.in","r",stdin);
scanf("%d", &n);
max=0;
int x[v];
long a[v];
q=-1;
for (int i=0; i<n; i++)
    {
    scanf("%ld", &a[i]);
    b[a[i]][++b[a[i]][0]]=i;
    if (x[a[i]]==0)
       {
       c[++q]=a[i];
       x[a[i]]=1;  
       }
    if (a[i]>max)
       max=a[i];
    }
fclose(stdin);
}

void radx(long max,long zero[v],long n)
{
long z,u,j;
int unu[v];
for (long i=0; i<max; i++)
    {
    z=-1;
    u=-1;
    for (j=0; j<n; j++)
	{
	if (((zero[j] >> i) &1)==0)
	   zero[++z]=zero[j];
	   else unu[++u]=zero[j];
	}
    u=-1;
    for (j=z+1; j<n; j++)
	zero[j]=unu[++u];
    }
}

int nr_pasi(long max1)
{
int pas=0;
while (max1>0)
      {
      ++pas;
      max1>>=1;
      }
return pas;
}

void verifica(long d)
{
if (d-inc+1<l)     
   l=d-inc+1;
}    

void rezolvare(long e,long d)
{
if (e>q)
   verifica(d);
   else for (long i=1; i<=b[c[e]][0]; i++)
	    {
	    if (e==0)
	       inc=b[c[e]][i];
	    if (b[c[e]][i]>d)
	       rezolvare(e+1,b[c[e]][i]);
    }
}

void scriere()
{
freopen("secv.out","w",stdout);
if (l==6000)
   printf("-1");
   else printf("%d", l);
fclose(stdout);
}

int main()
{
l=6000;
citire();    
max=nr_pasi(max);
radx(max,c,q+1);
rezolvare(0,0);
scriere();
return 0;
}