#include <bits/stdc++.h>
using namespace std;
#include <atcoder/modint>
using namespace atcoder;
using mint = modint998244353;
//using mint = modint1000000007;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using tlll = tuple<ll, ll, ll>;
constexpr ll INF = 1LL << 60;
template<class T> bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;}
template<class T> bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;}
ll safemod(ll A, ll M) {return (A % M + M) % M;}
ll divfloor(ll A, ll B) {if (B < 0) {return divfloor(-A, -B);} return (A - safemod(A, B)) / B;}
ll divceil(ll A, ll B) {if (B < 0) {return divceil(-A, -B);} return divfloor(A + B - 1, B);}
#define FINALANS(A) do {cout << (A) << '\n'; exit(0);} while (false)

#include <atcoder/scc>

int main()
{
  ll N, M;
  cin >> N >> M;
  vector<ll> A(M), B(M);
  for (ll i = 0; i < M; i++)
  {
    cin >> A.at(i) >> B.at(i);
    A.at(i)--, B.at(i)--;
  }

  scc_graph gr(N);
  for (ll i = 0; i < M; i++)
  {
    ll a = A.at(i), b = B.at(i);
    gr.add_edge(a, b);
  }

  auto scc = gr.scc();
  ll K = scc.size();
  if (K == 1)
    FINALANS(0);
  vector<ll> invs(N);
  for (ll i = 0; i < K; i++)
  {
    for (auto v : scc.at(i))
    {
      invs.at(v) = i;
    }
  }

  vector<ll> in(K, 0), out(K, 0);
  for (ll i = 0; i < M; i++)
  {
    ll a = A.at(i), b = B.at(i);
    ll c = invs.at(a), d = invs.at(b);
    if (c != d)
      out.at(c)++, in.at(d)++;
  }

  ll x = count(in.begin(), in.end(), 0LL);
  ll y = count(out.begin(), out.end(), 0LL);
  ll ans = max(x, y);
  cout << ans << endl;
}