#include<stdio.h>
#include<algorithm>
#include<assert.h>
using namespace std;

FILE *f = fopen("secv.in","r");
FILE *g = fopen("secv.out","w");

#define MaxN 5010

int N,Nr,Max,Sol,poz;
int A[MaxN];
int Best[MaxN],Poz[MaxN];

void citire(void)
{
	fscanf(f,"%d ",&N);
	for(int i=1;i<=N;i++)
		fscanf(f,"%d ",&A[i]);
}

void NumereUnice(void)
{
	int C[MaxN] = {-1};
	
	for(int i=1;i<=N;i++)
		C[i] = A[i];
	
	sort(C+1,C+N+1);
	
	for(int i=1;i<=N;i++)
		if(C[i] != C[i-1])
			++ Nr;
}

void Rezolvare(void)
{
	NumereUnice();
	
	for(int i=1;i<=N;i++)
	{
		Best[i] = 1; Poz[i] = i;
		
		for(int j=i-1;j;j--)
			if(A[j] < A[i] && (Best[j]+1 > Best[i] || (Best[j]+1 == Best[i] && Poz[j] > Poz[i])))
				Best[i] = Best[j]+1, Poz[i] = Poz[j];
				
		//printf("%d ",Best[i]);		
		
		if(Best[Max] < Best[i] || (Best[Max] == Best[i] && Poz[i] > Poz[Max]))
			Max = i ,Sol = i-Poz[i]+1;
	}
	
	if(Best[Max] != Nr)
		Sol = -1;
		
	assert(Sol != -1);
}

int main()
{
	citire();
	Rezolvare();
	
	fprintf(g,"%d\n",Sol);
}