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

vector< vector<int> > g, gr;
vector<char> used;
vector<int> order, component;

void dfs1(int v) {
        used[v] = true;
        for (size_t i = 0; i < g[v].size(); i++)
                if (!used[ g[v][i] ])
                        dfs1( g[v][i] );
        order.push_back(v);
}

void dfs2(int v) {
        used[v] = true;
        component.push_back(v);
        for (size_t i = 0; i < gr[v].size(); i++)
                if (!used[ gr[v][i] ])
                        dfs2( gr[v][i] );
}

int main() {
        int n, m;
        cin >> n >> m;
        g.assign(n, vector<int>());
        gr.assign(n, vector<int>());
        for (int i = 0; i < m; i++) {
                int v, u;
                cin >> v >> u;
                v--; u--;
                g[v].push_back(u);
                gr[u].push_back(v);
        }

        used.assign(n, false);
        for (int i = 0; i < n; i++)
                if (!used[i])
                        dfs1(i);

        int count = 0;
        used.assign(n, false);
        for (int i = 0; i < n; i++) {
                int v = order[n-1-i];
                if (!used[v]) {
                        dfs2(v);
                        if (component.size() > 0) {
                                count++;
                        }
                        component.clear();
                }
        }
        cout << count;
        return 0;
}