import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Template {
	public static void main(String[] args) {
		List<Integer> cardList = new ArrayList<Integer>();
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		for(int i = 0; i < n; i++){
			cardList.add(i + 1);
		}
		for(int i = 0; i < m; i++){
			int a = sc.nextInt();
			cardList.add(0, cardList.get(a - 1));
			cardList.remove(a);
		}
		sc.close();
		System.out.println(cardList.get(0));
	}
}