#define MAX_N 100000
#define INF 0x3f3f3f3f

#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

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

int n, m, ctc, t, timp[MAX_N + 1];
vector<int> G[MAX_N + 1];

int Df(int nod);

int main()
{
    fin >> n >> m;

    for (int i = 1, x, y; i <= m; ++i)
    {
        fin >> x >> y;
        G[x].push_back(y);
    }

    for (int i = 1; i <= n; ++i)
    {
        if (timp[i] == 0)
        {
            Df(i);
        }
    }

    fout << ctc;

    fin.close();
    fout.close();
    return 0;
}

int Df(int nod)
{
    int res = INF;
    timp[nod] = ++t;

    for (int vecin : G[nod])
    {
        if (timp[vecin] == 0)
        {
            res = min(res, Df(vecin));
        }
        else
        {
            res = min(res, timp[vecin]);
        }
    }

    if (res == timp[nod])
    {
        ++ctc;
    }

    res = min(res, timp[nod]);
    return res;
}