import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		//your code here
                Scanner sc = new Scanner(System.in);
                int n = sc.nextInt();
                int[] arr = new int[n];
                for(int i = 0; i < n; i++) arr[i] = sc.nextInt();
                
               int mx = Integer.MIN_VALUE;
                int[] lf = new int[n];
               for(int i = 0; i < n; i++){
                     mx= Math.max(mx, arr[i]);
                       lf[i] = mx;
               }
                int mn = Integer.MAX_VALUE;
                int[] rf = new int[n];
                for(int i= n-1; i>= 0; i--){
                        mn = Math.min(mn, arr[i]);
                        rf[i] = mn;
                }
                int  id = -1;
                for(int i = 0; i< n; i++){
                        if(rf[i] == lf[i] && lf[i] == arr[i]){
                                id= i;
                                break;
                        }
                }
                System.out.println(id);
	}
}