#include <fstream>
#include <stack>
#include <vector>

int main() {
  std::ifstream in("dfs.in");
  std::ofstream out("dfs.out");
  
  int n, m;
  in >> n >> m;
  
  std::vector<std::vector<int>> graph;
  std::vector<bool> visited;
  graph.reserve(n);
  visited.reserve(n);
  for (int i = 0; i < n; i++) {
    graph.push_back(std::vector<int>());
    visited.push_back(false);
  }
  
  for (int i = 0; i < m; i++) {
    int from, to;
    in >> from >> to;
    graph[from - 1].push_back(to);
  }
  
  int numComponents = 0;
  for (int i = 1; i <= n; i++) {
    if (!visited[i - 1]) {
      numComponents++;
      std::stack<int> s;
      s.push(i);
      visited[i - 1] = true;
      while (!s.empty()) {
        int u = s.top();
        bool hasAnyNeighbors = false;
        for (int v : graph[u - 1]) {
          if (!visited[v - 1]) {
            visited[v - 1] = true;
            s.push(v);
            hasAnyNeighbors = true;
            break;
          }
        }
        if (!hasAnyNeighbors) s.pop();
      }
    }
  }
  
  out << numComponents;
  
  return 0;
}