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

using namespace std;

unsigned int N, M, compConexe;
unsigned const int NMAX = 100005;

vector<unsigned int> muchii[NMAX];

bool vizitat[NMAX]{false};

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

void DFS(unsigned int nod)
{
    vizitat[nod] = true;
    for(unsigned int i = 0; i < muchii[nod].size(); i++)
    {
        unsigned int Vecin = muchii[nod][i];
        if(!vizitat[Vecin])
            DFS(Vecin);
    }
}

int main()
{
    fin >> N >> M;

    for(unsigned int i = 0; i < M; i++)
    {
        unsigned int X, Y;
        fin >> X >> Y;
        muchii[X].push_back(Y);
    }

    fin.close();

    for(unsigned int i = 0; i < N; i++)
    {
        if(!vizitat[i])
        {
            compConexe++;
            DFS(i);
        }
    }

    fout << compConexe;
    fout.close();

    return 0;
}