import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class JengaSort {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		List<Integer> list = new ArrayList<Integer>();
		for (int i = 0; i < N; i++) {
			list.add(sc.nextInt());
		}
		int base = list.get(N - 1);

		int count = 0;
		for (int i = N-1; i > 0; i--) {
			int next = list.get(i - 1);
			if (next == base - 1) {
				base = next;
			} else {
				count++;
			}
		}
		System.out.println(count);

	}
}