#include <fstream>
#include <vector>

using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");

int N,M;
int nrcomponente;

struct Nod
{
  vector <int> Ad;

  int component=0;
};

Nod A[100002];

void Read()
{
  fin>>N>>M;

  int x,y;

  for(int i=1; i<=M; ++i)
  {
    fin>>x>>y;
    A[x].Ad.push_back(y);
  }

  fin.close();
}

void DFS(int nod)
{
  A[nod].component=nrcomponente;

  for(int i=0; i<A[nod].Ad.size(); ++i)
    if(A[A[nod].Ad[i]].component==0)
     DFS(A[nod].Ad[i]);

}

void Do()
{
  for(int i=1; i<=N; ++i)
    if(A[i].component==0)
     ++nrcomponente,
     DFS(i);
}

void Print()
{
  fout<<nrcomponente<<'\n';

  fout.close();
}

int main()
{
   Read();
   Do();
   Print();

    return 0;
}