#include <iostream>
#include <vector>
#include <unordered_map>
#include <atcoder/dsu.hpp>

using namespace std;
using namespace atcoder;
using ll = long long;

int main() {
  ll n, m;
  cin >> n >> m;
  vector<ll> in(n), out(n);
  dsu d(n);
  for (ll i = 0; i < m; i++) {
    ll u, v;
    cin >> u >> v;
    u--; v--;
    out[u]++;
    in[v]++;
    d.merge(u, v);
  }

  unordered_map<ll, ll> ind;
  for (ll i = 0; i < n; i++)
    ind[d.leader(i)] += max(0LL, in[i] - out[i]);

  ll ans = 0;
  for (auto& [k, v] : ind) {
    ans += max(1LL, v);
  }
  cout << max(0LL, ans - 1) << "\n";
}