#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;

int N, M;
vector<int> G[110];
int indegree[110];
int cnt;

int main() {
  cin >> N >> M;
  for (int i = 1; i <= M; i++) {
    int a, b; cin >> a >> b;
    G[a].push_back(b);
    indegree[b]++;
  }
  for (int i = 1; i <= N; i++) {
    if (indegree[i] == 0) cnt++;
  }
  cout << cnt << endl;
  return 0;
}