#include <bits/stdc++.h>
using namespace std;
struct strongly_connected_components{
	vector<vector<int>> ans;
	vector<int> scc;
	void dfs1(vector<vector<int>> &E, vector<int> &t, vector<bool> &used, int v){
		for (int w : E[v]){
			if (!used[w]){
				used[w] = true;
				dfs1(E, t, used, w);
			}
		}
		t.push_back(v);
	}
	void dfs2(vector<vector<int>> &E2, vector<bool> &used2, int v){
		ans.back().push_back(v);
		for (int w : E2[v]){
			if (!used2[w]){
				used2[w] = true;
				dfs2(E2, used2, w);
			}
		}
	}
	strongly_connected_components(vector<vector<int>> &E){
		int N = E.size();
		vector<vector<int>> E2(N);
		for (int i = 0; i < N; i++){
			for (int j : E[i]){
				E2[j].push_back(i);
			}
		}
		vector<int> t;
		vector<bool> used(N, false);
		for (int i = 0; i < N; i++){
			if (!used[i]){
				used[i] = true;
				dfs1(E, t, used, i);
			}
		}
		reverse(t.begin(), t.end());
		vector<bool> used2(N, false);
		scc = vector<int>(N);
		int cnt = 0;
		for (int i = 0; i < N; i++){
			if (!used2[t[i]]){
				used2[t[i]] = true;
				ans.push_back(vector<int>());
				dfs2(E2, used2, t[i]);
				for (int j : ans.back()){
					scc[j] = cnt;
				}
				cnt++;
			}
		}
	}
	int operator [](int k){
		return scc[k];
	}
	int size(){
		return ans.size();
	}
};
int main(){
  int N, M;
  cin >> N >> M;
  vector<vector<int>> E(N);
  for (int i = 0; i < M; i++){
    int A, B;
    cin >> A >> B;
    A--;
    B--;
    E[A].push_back(B);
  }
  strongly_connected_components G(E);
  int V = G.size();
  if (V == 1){
    cout << 0 << endl;
  } else {
    vector<vector<int>> E2(V);
    vector<bool> ok1(V, false);
    vector<bool> ok2(V, false);
    for (int i = 0; i < N; i++){
      for (int j : E[i]){
        if (G[i] != G[j]){
          E2[G[i]].push_back(G[j]);
          E2[G[j]].push_back(G[i]);
          ok1[G[i]] = true;
          ok2[G[j]] = true;
        }
      }
    }
    int ans = 0;
    vector<bool> used(V, false);
    for (int i = 0; i < V; i++){
      if (!used[i]){
        used[i] = true;
        int cnt1 = 0, cnt2 = 0;
        queue<int> Q;
        Q.push(i);
        while (!Q.empty()){
          int v = Q.front();
          Q.pop();
          if (!ok1[v]){
            cnt1++;
          }
          if (!ok2[v]){
            cnt2++;
          }
          for (int w : E2[v]){
            if (!used[w]){
              used[w] = true;
              Q.push(w);
            }
          }
        }
        ans += max(cnt1, cnt2);
      }
    }
    cout << ans << endl;
  }
}