import java.util.Scanner;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();
        int[] ind = new int[N];
        int ans = N;
        while(M-->0){
            sc.next();
            int B = sc.nextInt()-1;
            if(ind[B]++==0)
                --ans;
        }
        System.out.println(ans);
    }
}