#include<fstream>

using namespace std;
ifstream in ("secv.in");
ofstream out ("secv.out");
int t,maxi,p,n,j,i,k=0,pp[5002],minime[5002],sw,tat[5002];
long v[5002],a[5002];
int poz (long a[5002], int p, int u)
{
    int piv=a[p],aux;
    while (p<u)
    {
        if (a[p]>a[u])
        {
            aux=a[p];
            a[p]=a[u];
            a[u]=aux;
        }
        if (piv==a[p]) u--;
        else p++;
    }
    return p;
}

void quick(long a[5002], int p, int u)
{
    int k;
    if (p<u)
    {
        k=poz(a,p,u);
        quick(a,p,k-1);
        quick(a,k+1,u);
    }
}

int main()
{
    in>>n;
    for (i=1; i<=n; i++)
    in>>v[i];
    for (i=1; i<=n; i++)
    a[i]=v[i];
    quick(a,1,n);
    k=1;
    for (i=2; i<=n; i++)
    if (a[i]!=a[i-1])
    k++;
    minime[1]=pp[1]=1;
    tat[1]=0;
    for (i=2; i<=n; i++)
    {
        t=0;
        maxi=0;
        for (j=i-1; j>=1; j--)
        if (v[i]>v[j] && maxi<minime[j])
            {
                maxi=minime[j];
                t=j;
                p=pp[j];
            }
        if (maxi==0)
        {
            minime[i]=1;
            tat[i]=0;
            pp[i]=i;
        }
        else
        {
            minime[i]=minime[t]+1;
            tat[i]=t;
            pp[i]=p;
        }
    }
    int min=5001;
    for (i=n; i>=k; i--)
        if (minime[i]==k && i-pp[i]+1<min) min=i-pp[i]+1;

    if (min<5001) out<<min;
    else out<<-1;

    return 0;
}