import java.util.*;
public class Main {
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
int n=sc.nextInt();
int[]arr=new int[n];
for(int i=0;i<arr.length;i++){
arr[i]=sc.nextInt();
}
int item=sc.nextInt();
System.out.println(Binary(arr,item));
}
public static int Binary(int[]arr,int item){
int lo=0;
int hi=arr.length-1;
while(lo<=hi){
int mid = (lo+hi)/2;
if(arr[mid]<item){
lo=mid+1;
}else if(arr[mid]>item){
hi=mid-1;
}else{
return mid;
}
}
return -1;
}
}