#include <iostream>
#include <algorithm>
#include <random>
#include <stack>

using namespace std;

int main() {
    int n, m; 
    cin >> n >> m;
    vector<vector<int>> adj(n, vector<int>());
    vector<vector<int>> back_adj(n, vector<int>());
    for(int i = 0; i < m; i++) {
        int a, b; cin >> a >> b;
        a--;
        b--;
        adj[b].push_back(a);
        back_adj[a].push_back(b);
    }
    vector<int> component(n, 0);
    vector<int> nodes(n, 0);
    for(int i = 0; i < n; i++) {
        nodes[i] = i;
    }
    auto rng = default_random_engine{};
    shuffle(begin(nodes), end(nodes), rng);

    int num_components = 0;

    for(int root : nodes) {
        if(component[root] <= 0) {
            num_components++;
            component[root] = -num_components;
            stack<int> s;
            s.push(root);
            while(!s.empty()) {
                int cur = s.top();
                s.pop();
                for(int nb : adj[cur]) {
                    if(component[nb] <= 0 && component[nb] != -num_components) {
                        component[nb] = -num_components;
                        s.push(nb);
                    }
                }
            }
            component[root] = num_components;
            s.push(root);
            while(!s.empty()) {
                int cur = s.top();
                s.pop();
                for(int nb : back_adj[cur]) {
                    if(component[nb] == -num_components) {
                        component[nb] = num_components;
                        s.push(nb);
                    }
                }
            }
        }
    }

    
    vector<int> dag_out_edges(num_components, 0);
    for(int i = 0; i < n; i++) {
        for(int nb : adj[i]) {
            if(component[i] != component[nb]) {
                dag_out_edges[component[i] - 1]++;
            }
        }
    }

    int result = 0;
    for(int ct : dag_out_edges) {
        result += (ct == 0);
    }
    cout << result << endl;
}