#include<stdio.h>
#include<string.h>
#define val 5002

long a[val],max,b[val],w[val],p;
int n,q;

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

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

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

void rezolvare()
{
long o,e;
for (int i=0; i<n; i++)
    {
    if (b[a[i]]>=0 && a[i]==w[0])
       {
       o=1;
       e=0;
       for (int j=i+1; j<n; j++)
	   if (b[a[j]]>=0 && w[e+1]==a[j])
	      {
	      ++e;
	      o=j;
              }
       o=o-i+1;
       if (o<max && e-1==q)
          max=o;
       }
    }
}

void printare()
{
freopen("secv.out","w",stdout);
if (max>1)
   printf("%ld", max);
   else printf("-1");
fclose(stdin);     
}     

int main()
{
memset(b,0xff,sizeof(b));
citire();
max=nr_pasi(max);
radx(max,w,q+1);
max=-1;
rezolvare();
printare();
return 0;
}