import java.util.*;

public class _10775 {
    static int[] parents;
    static int ans = 0;

    static int find(int x) {
        if(parents[x] != x) return parents[x] = find(parents[x]);
        return parents[x]; 
    }

    static void union(int x, int y) {
        x = find(x);
        y = find(y);

        if(x > y) {
            int temp = x;
            x = y;
            y = temp;
        }

        parents[y] = x;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int G = sc.nextInt(), P = sc.nextInt();
        parents = new int[G+1];
        for(int i=1; i<=G; i++) parents[i] = i;

        for(int i=0; i<P; i++) {
            int gi = sc.nextInt();
            gi = find(gi);
            
            if(gi == 0) break;

            union(gi, gi-1);
            ans++;
        }
        System.out.println(ans);

        sc.close();
    }    
}