#include<iostream>
#include<fstream>
using namespace std;
ifstream f("secv.in");
ofstream g("secv.out");
long int v[5001],u[5001];
int N,i,j;
int main()
{f>>N;
int ok=1;
for(i=1;i<=N;i++) f>>v[i];
for(i=1;i<N;i++)
for(j=i+1;j<=N;j++)
if(v[i]<v[j]) {u[i]++; ok=1;}
else if(v[i]>=v[j]) ok=0;
int max=u[1],min=u[1],p=1,q=1;
for(i=2;i<=N;i++)
if(u[i]>max) {max=u[i]; p=i;}
else if(u[i]<=min) {min=u[i];q=i;}
if(ok==0) g<<-1;
else g<<q-p+1;
f.close(); g.close(); return 0;}