#include <iostream>
#include <vector>
#include <fstream>

#define NMAX 100000

using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");

int main() {
    int n, m;
    fin >> n >> m;

    vector<int> adj[NMAX];
    for (int i = 1; i <= m; i++) {
        int node_in, node_out;
        fin >> node_in >> node_out;
        adj[node_in].push_back(node_out);
    }


    int nr_componente = 0;
    vector<int> in_edge(n + 1, 0);

    // find the starting position
    for (int i = 1; i <= n; i++) {
        for (auto out_node : adj[i])
            in_edge[out_node]++;
    }
    for (int i = 1; i <= n; i++) {
        if (in_edge[i] == 0) {
            nr_componente++;
        }
    }
    fout << nr_componente;
}