#include <iostream>
#include <fstream>
using namespace std;

struct dfs
{
    long* urmasi;
    long cat;
    bool vizitat;

};

dfs* vector;

void adauga(long a, long b)
{
    vector[a].urmasi[++vector[a].cat] = b;
}

void depth(long a)
{
    if (vector[a].vizitat)
        return;
    for (long i = 1; i <= vector[a].cat; i++)
        depth(vector[a].urmasi[i]);
    vector[a].vizitat = true;
}

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

    long n, m;

    in >> n >> m;

    vector = new dfs[n];

    for (long i = 0; i < n; i++)
    {
        vector[i].cat = 0;
        vector[i].urmasi = new long[m - 1];
        vector[i].vizitat = false;
    }
    for (long i = 0; i < m; i++)
    {
        long unde, pecine;
        in >> unde >> pecine;
        unde--, pecine--;
        adauga(unde, pecine);
    }
    long contor = 0;

    for (long i = 0; i < n; i++)
        if (!vector[i].vizitat)
            depth(i), contor++;

    out << contor;
    return 0;
}