import java.util.*;
public class Main {
public static int linearSearch(int[] arr, int data) {
for (int i = 0; i < arr.length; i++) {
if(data==arr[i]) {
return i;
}
}
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 = linearSearch(arr, data);
if (index < 0) {
System.out.println(index);
} else {
System.out.println(index);
}
}
}