#include <fstream>
#include <vector>
using namespace std;

void dfs(
        const size_t v,
        vector<size_t>& visited,
        const vector<vector<size_t>>& G) {
    visited[v] = 1;
    for (int u : G[v]) if (!visited[u]) {
        dfs(u, visited, G);
    }
}

int connected_components(const vector<vector<size_t>>& G) {
    vector<size_t> visited(G.size(), 0);
    int n = 0;
    
    for (size_t v = 0; v < G.size(); ++v) if (!visited[v]) {
        ++n;
        dfs(v, visited, G);
    }
    
    return n;
}

int main() {
    ifstream fin("dfs.in");
    ofstream fout("dfs.out");
    
    int n, m;
    fin >> n >> m;
    
    vector<vector<size_t>> G(n);
    for (; m; --m) {
        int u, v;
        fin >> u >> v;
        G[u-1].push_back(v-1);
    }
    
    fout << connected_components(G) << endl;
    
    return 0;
}