public class App20_HelpRahulToSearch {
public static int binarySearch(int[] arr , int data) {
int low=0;
int high=arr.length-1;
while(low<=high) {
int mid = (low+high)/2;
if(data>arr[mid]) {
low=mid+1;
}
else if(data<arr[mid]){
high=mid-1;
}
else {
return mid;
}
}
return -1;
}
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 data = sc.nextInt();
int index = binarySearch(arr,data);
if (index < 0) {
System.out.println(index);
} else {
System.out.println(index);
}
}
}