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

using namespace std;

const int NMAX = 100000;

vector<int> g[NMAX];

bool d[NMAX];

void dfs(int root) {
   stack<int> s;
   s.push(root);

   while (!s.empty()) {
      int node = s.top();
      s.pop();
      d[node] = true;
      for (int v : g[node]) {
         if (!d[v]) {
            s.push(v);
         }
      }
   }
}

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

   int N, M;
   iff >> N >> M;
   for (int i = 0; i <= N; ++i) {
      d[i] = false;
   }

   for (int i = 0; i < M; ++i) {
      int n1, n2;
      iff >> n1 >> n2;
      g[n1].push_back(n2);
   }

   int count = 0;
   for (int i = 1; i <= N; ++i) {
      if (!d[i]) {
         dfs(i);
         count += 1;
      }
   }

   off << count;
   return 0;
}