#include <bits/stdc++.h>
using namespace std;

class Task {
public:
    void solve() {
        read_input();
        print_output(get_result());
    }

private:
    // numarul maxim de noduri
    static constexpr int NMAX = (int)1e5 + 5; // 10^5 + 5 = 100.005

    // n = numar de noduri, m = numar de muchii/arce
    int n, m;

    // adj[node] = lista de adiacenta a nodului node
    // exemplu: daca adj[node] = {..., neigh, ...} => exista arcul (node, neigh)
    vector<int> adj[NMAX];

    void read_input() {
        ifstream fin("dfs.in");
        fin >> n >> m;
        for (int i = 1, x, y; i <= m; i++) {
            fin >> x >> y; // arc (x, y)
            adj[x].push_back(y);
        }
        fin.close();
    }

    void dfs(int node, vector<int>& start, int& timestamp) {
        start[node] = timestamp;
        timestamp++;
        for (int neigh : adj[node]) {
            if (start[neigh] == 0) {
                start[neigh] = timestamp;
                dfs(neigh, start, timestamp);
                timestamp++;
            }
        }
    }

    int get_result() {
        // TODO: Faceti sortarea topologica a grafului stocat cu liste de adiacenta din adj.
        // *******
        // ATENTIE: nodurile sunt indexate de la 1 la n.
        // *******
        vector<int> start(n + 1, 0);

        int time = 1;
        int nr_elem_con = 0;

        for (int i = 1; i <= n; i++) {
            if (start[i] == 0) {
                nr_elem_con++;
                dfs(i, start, time);
            }
        }
        return nr_elem_con;
    }

    void print_output(int nr) {
        ofstream fout("dfs.out");
        fout << nr;
        fout.close();
    }
};

// [ATENTIE] NU modifica functia main!
int main() {
    // * se aloca un obiect Task pe heap
    // (se presupune ca e prea mare pentru a fi alocat pe stiva)
    // * se apeleaza metoda solve()
    // (citire, rezolvare, printare)
    // * se distruge obiectul si se elibereaza memoria
    auto* task = new (nothrow) Task(); // hint: cppreference/nothrow
    if (!task) {
        cerr << "new failed: WTF are you doing? Throw your PC!\n";
        return -1;
    }
    task->solve();
    delete task;
    return 0;
}