#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
long long primeNumber(long long x) {
  bool fire = true;
  for(int i = 2; i <= sqrt(x); i++) {
    if(x % i == 0) {
      fire = false;
    }
  }
  return fire;
}
int main() {
    int N, M; cin >> N >> M;
    map<int,int> dic;
    Graph G(N + 1);
    for (int i = 0; i < M; ++i) {
        int a, b; cin >>a >> b;
      dic[b]++;
    }
  int ans = 0;
  for(int i = 1; i <= N; i++) {
    if(dic[i] == 0) {
      ans++;
    }
  }
  cout <<ans << endl;
}