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