import java.util.*;

public class BinarySearchDemo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        Arrays.sort(a);
        int target = sc.nextInt();
        int idx = Arrays.binarySearch(a, target);
        System.out.println(idx >= 0 ? idx : -1);
        sc.close();
    }
}