/* -*- coding: utf-8 -*-
 *
 * 2052.cc:  No.2052 Indegree - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_N = 100;

/* typedef */

/* global variables */

int ids[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);

  for (int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    ids[v]++;
  }

  int c = 0;
  for (int i = 0; i < n; i++)
    if (ids[i] == 0) c++;

  printf("%d\n", c);
  return 0;
}