#include<stdio.h>
#define N 5001
long a[N],b[N],p[N],i,j,k,c,m,n,u,v; 
int main()
{freopen("secv.in","r",stdin);
freopen("secv.out","w",stdout);
scanf("%ld\n",&n);
a[0]=b[0]=m=0;
for(i=1;i<=n;i++)
       {scanf("%ld",&a[i]);
       if(a[b[m]]<a[i])
              {p[i]=b[m];
              b[++m]=i;}
       for(j=0,k=m;j<k;)
              {c=(j+k)/2;
              if(a[b[c]]<a[i])
                     j=c+1;
              else
                     k=c;}
       if(a[i]<a[b[j]])
              {if(j>0)
                     p[i]=b[j-1];
              b[j]=i;}}
for(u=m,v=b[m];u--;v=p[v])
       b[u]=v;
if(m==0)
       printf("-1\n");
else
       printf("%ld\n",b[m-1]-b[0]);
fclose(stdin);
fclose(stdout);
return 0;}