#include<cstdio>
#include<algorithm>
#define INF 10000

using namespace std;

int v[5002],c[5002],a[5002],i,j=1,n,m,x,minim=INF,k;

int main()
{       freopen("secv.in","r",stdin);
        freopen("secv.out","w",stdout);
        scanf("%d",&n);
        for(i=1;i<=n;i++)v[i]=c[i]=a[i]=-1;
        for(i=1;i<=n;i++)
        {       scanf("%d",&a[i]);
                v[i]=a[i];
        }
        sort(v+1,v+n+1);
        for(i=1;i<=n;i++)
                if(v[i]!=c[j-1]) c[j++]=v[i];
        --j;m=j;
        for(x=1;x<=n;x++)
                if(a[x]==c[1])
                {       k=0;
                        for(j=1,i=x;j<=m&&i<=n;)
                                if(a[i]==c[j]) {j++;i++;k++;}
                                else {i++;k++;}
                        if(j==m+1&&k<minim) minim=k;
                }
        if(minim!=INF) printf("%d\n",minim);
        else printf("-1\n");
        return 0;
}