import java.util.Scanner;
import javax.lang.model.util.ElementScanner14;
public class Lastindexchallenge
{
static Scanner scn=new Scanner(System.in);
public static void main(String[] args)
{
int[] arr=takeinput();
int M=scn.nextInt();
System.out.println(lastIndex(arr, 0, M));
}
public static int[] takeinput()
{
int N =scn.nextInt();
if(1<N && N<1000)
{
int[] arr=new int[N];
for(int i=0;i<arr.length;i++)
{
arr[i]=scn.nextInt();
}
return arr;
}
else
{
int[] base=new int[0];
return base;
}
}
public static int lastIndex(int[] arr, int i, int data)
{
if(arr.length==i)
{
return -1;
}
int index=lastIndex(arr, i+1, data);
if(index==-1)
{
if(arr[i]==data)
{
return i;
}
else
{
return -1;
}
}
else
{
return index;
}
}
}