#include <algorithm>
#include <iostream>
#include <vector>
#include <stack>

using std::vector;
using std::stack;

void dfs(vector<vector<int> > &adj, vector<bool> &visited, stack<int> &order, int v) {
    visited[v] = true;
    int s = adj[v].size();
    for (int j = 0; j < s; j++) {
        int w = adj[v][j];
        if (!visited[w])
            dfs(adj, visited, order, w);
    }
    order.push(v);
}

void dfs(vector<vector<int> > &adj, vector<bool> &visited, int v) {
    visited[v] = true;
    int s = adj[v].size();
    for (int j = 0; j < s; j++) {
        int w = adj[v][j];
        if (!visited[w])
            dfs(adj, visited, w);
    }
}

int number_of_strongly_connected_components(vector<vector<int> > adj) {
    int result = 0;

    vector<vector<int> > radj(adj.size(), vector<int>());
    for (size_t i = 0; i < adj.size(); i++)
        for (size_t j = 0; j < adj[i].size(); j++)
            radj[adj[i][j]].push_back(i);

    stack<int> order;
    vector<bool> visited(radj.size(), 0);

    for (size_t i = 0; i < adj.size(); i++)
        if (!visited[i])
            dfs(adj, visited, order, i);

    for (size_t i = 0; i < visited.size(); i++)
        visited[i] = false;

    while(!order.empty()) {
        int v = order.top();
        order.pop();
        if (!visited[v]) {
            result += 1;
            dfs(radj, visited, v);
        }
    }

    return result;
}

int main() {
  size_t n, m;
  std::cin >> n >> m;
  vector<vector<int> > adj(n, vector<int>());
  for (size_t i = 0; i < m; i++) {
    int x, y;
    std::cin >> x >> y;
    adj[x - 1].push_back(y - 1);
  }
  std::cout << number_of_strongly_connected_components(adj) << '\n';
}