#include <fstream>
#include <bits/stdc++.h>

using namespace std;

vector<int> adj[100000];
bool  visited[100000];

void dfs(int v) {
    visited[v] = true;
    for (auto m : adj[v]) {
        if (!visited[m])
            dfs(m);
    }
}

int main() {
    ifstream in("dfs.in");
    ofstream out("dfs.out");

    int n, m;
    in >> n >> m;

    for (int i = 0; i < m; i++) {
        int x, y;
        in >> x >> y;
        adj[y].push_back(x);
    }

    int comp = 0;
    for (int i = 0; i < n; i++) {
        if (!visited[i]) {
            comp++;
            dfs(i);
        }

    }
    
    out << comp;

    in.close();
    out.close();
    return 0;
}