#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n, m;
  cin >> n >> m;
  vector<int> indeg(n, 0);
  rep(_, m) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    indeg[v]++;
  }
  int ans = 0;
  rep(i, n) if (indeg[i] == 0) ans++;
  cout << ans << endl;
  return 0;
}