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 < n ; i++){
arr[i] = sc.nextInt();
}
int item = sc.nextInt();
System.out.println(search( arr , item));
}
public static int search(int[] arr, int item){
int lo = 0;
int hi = arr.length - 1;
while(lo <= hi){
int mid = (lo + hi) / 2;
if(arr[mid] > item) hi = mid - 1;
else if(arr[mid] < item) lo = mid + 1;
else return mid;
}
return -1;
}
}