import java.util.ArrayList;
import java.util.Scanner;
public class No123 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int n = s.nextInt() , m = s.nextInt();
		ArrayList al = new ArrayList();
		for(int i = 0;i < n;i++){
			al.add(n - i);
		}

		for(int i = 0;i < m;i++){
			int a = s.nextInt() , get = (int)al.get(n - a);
			al.remove(n - a);
			al.add(get);
		}
		System.out.println(al.get(n - 1));

	}

}