import java.util.Scanner;
public class Main{
public static Scanner s=new Scanner(System.in);
public static void main(String[] args)
{
int [] array=takeinput();
System.out.println(Index(array));
}
public static int [] takeinput(){
int n=s.nextInt();
int [] arr=new int[n];
for(int i=0;i<n;i++)
{
arr[i]=s.nextInt();
}
return arr;
}
public static int Index(int [] arr)
{
int m=s.nextInt();
int low=0;
int high=arr.length-1;
while(low<=high){
int mid=(low+high)/2;
if(arr[mid]>m)
{
low=mid+1;
}
else if (arr[mid]<m)
{
high=mid-1;
}
else{
return mid;
}
}
return -1;
}
}