#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int v[5005],v1[5005],vc[5005],b[5005],k;
int bs(int val)
{
    int med,st,dr;
    st=1;
    dr=k;
    while (st<=dr)
    {
        med=(st+dr)/2;
        if (vc[med]==val)
            return med;
        else if(vc[med]<val)
            st=med+1;
        else dr=med-1;
    }
    return 0;
}
int main()
{
    freopen("secv.in","r",stdin);
    freopen ("secv.out","w",stdout);
    int n,i,j,lmin,l,val;
    scanf ("%d",&n);
    for (i=1;i<=n;i++) {
        scanf ("%d",&v[i]);
        v1[i]=v[i];
    }
    sort(v1+1,v1+n+1);
    k=1;vc[k]=v1[k];
    int last=v1[k];
    for (i=2;i<=n;i++)
        if (v1[i]!=last) {
            vc[++k]=v1[i];
            last=v1[i];
        }
    for (i=1;i<=n;i++)
        b[i]=bs(v[i]);
    lmin=n+5;
    for (i=1;i<=n;i++)
        if (v[i]==1)
        {
            val=2;
            for (j=i;j<=n;j++)
                if (v[j]==val)
                {
                    val++;
                    if (val==k+1)
                    {
                        l=j-i+1;
                        if (l<lmin)
                            lmin=l;
                        break;
                    }
                }
        }
    if(n!=1) {
        if(lmin!=n+5)
            printf("%d",lmin);
        else printf("-1");
    }else printf("1");    
    return 0;
}