#include <bits/stdc++.h>
using namespace std;
#define in ({int x=0;int c=getchar(),n=0;for(;!isdigit(c);c=getchar()) n=(c=='-');for(;isdigit(c);c=getchar()) x=x*10+c-'0';n?-x:x;})
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//mt19937 rng(1012);
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define fasty ios_base::sync_with_stdio(0),cin.tie(0);
#define forinc(a,b,c) for(int a=b,_c=c;a<=_c;++a)
#define fordec(a,b,c) for(int a=b,_c=c;a>=_c;--a)
#define forv(a,b) for(auto&a:b)
#define fi first
#define se second
#define pb push_back
#define ii pair<int,int>
#define mt make_tuple
#define all(a) a.begin(),a.end()
#define reset(f, x) memset(f, x, sizeof(f))
#define gg exit(0);
#ifndef UNX
#include "prize.h"
#endif // UNX
const int N=200010;
int n,asked;
vector<int> dd[N];
#ifdef UNX
int arr[N];
vector<int> ask(int p){
asked++;
int x=0, y=0;
forinc(i,1,p) x+=arr[i]<arr[p+1];
forinc(i,p+2,n) y+=arr[i]<arr[p+1];
return {x,y};
}
#endif // UNX
vector<int> qry(int i){
return dd[i].size() ? dd[i] : dd[i]=ask(i-1);
}
int same(int i,int j){
auto x=qry(i), y=qry(j);
return x[0]+x[1]==y[0]+y[1];
}
int cnt(int i,int j){
if(i>j) swap(i,j);
auto x=qry(i), y=qry(j);
return y[0]-x[0];
}
int solve(int l){
int i=l, sz=0;
while(i<n){
fordec(j,17,0){
int t=i+(1<<j);
if(t>n) continue;
if(same(l,t) && cnt(l,t)==sz) i=t;
}
if(i==n) break;
auto a=qry(++i);
if(a[0]+a[1]==0) return i-1;
sz++;
}
i=l; int piv=sz;
while(i>1){
fordec(j,17,0){
int t=i-(1<<j);
if(t<1) continue;
if(same(l,t) && cnt(l,t)==sz-piv) i=t;
}
if(i==1) break;
auto a=qry(--i);
if(a[0]+a[1]==0) return i-1;
sz++;
}
auto a=qry(l);
//if(a[0]+a[1]+sz!=n) exit(-1);
return -1;
}
int find_best(int nn){
auto a=qry(1); n=nn;
if(a[0]+a[1]==0) return 0;
if(a[0]+a[1]==1){
int le=0,mi,ri=n-1;
while(le<=ri){
mi=(le+ri)/2;
a=qry(mi+1);
if(a[0]+a[1]==0) return mi;
if(a[0]) ri=mi-1; else le=mi+1;
}
}
int x,tmp=-1;
forinc(t,1,10){
int i=rnd(1,n);
auto a=qry(i);
if(tmp<a[0]+a[1]){
tmp=a[0]+a[1];
x=i;
}
}
if((n-tmp)+(n-tmp)<n) exit(-1);
return solve(x);
}
#ifdef UNX
main(){
#define task "TASK"
if(fopen(task".inp","r")){
freopen(task".inp","r",stdin);
//freopen(task".out","w",stdout);
}
n=in;
forinc(i,1,n) arr[i]=in;
cout<<find_best(n)<<"\n";
cerr<<asked;
}
#endif // UNX
